[42]" 42. What constitutes the ‘grounds’ for a directly discriminatory act will vary according to the type of case. The paradigm is perhaps the case where the discriminator applies a rule or criterion which is inherently based on the protected characteristic. In such a case the criterion itself, or its application, plainly constitutes the grounds of the act complained of, and there is no need to look further. But there are other cases which do not involve the application of any inherently discriminatory criterion and where the discriminatory grounds consist in the fact that the protected characteristic has operated on the discriminator's mind – what Lord Nicholls in Nagarajan called his ‘mental processes’ (p. 884 D-E) – so as to lead him to act in the way complained of. It does not have to be the only such factor: it is enough if it has had ‘a significant influence’. Nor need it be conscious: a subconscious motivation, if proved, will suffice. Both the latter points are established in the speech of Lord Nicholls in Nagarajan : see pp. 885-6.[43]The distinction between the two kinds of case is most authoritatively made in the judgment of Lady Hale in R (E) v Governors of the JFS [2010] 2 AC 728 , at paras. 61-64 (pp. 759-760), though it is to be found in the earlier case-law: I would venture to refer to my own judgment, sitting in the EAT, in Amnesty International v Ahmed [2009] ICR 1450 , at paras. 32-35 (pp. 1469-70). 44. The present case is plainly not of the ‘criterion’ type. Mr Robottom in his skeleton argument contended otherwise, but the contention is, with all respect to him, unsustainable. The various acts of which Ms Onu complains – underpayment, being required to work excessive hours etc. – are not inherently based on her immigration status. If her immigration status was (part of) the grounds for those acts it is only because, in the mental processes which led to their doing them, Mr and Mrs Akwiwu were significantly influenced by it." 31. It was not in dispute before me that this approach is appropriate in a direct discrimination claim under section 18 just as under section 13. I am sure that this is the case. There is, in fact, authority in the Employment Appeal Tribunal following this general approach: see Johal v Commissioner for Equality and Human Rights [2010] UKEAT/0541/09, HHJ Peter Clark. The question is whether the tribunal applied this approach. 32. I have reached the conclusion that the tribunal did not apply this approach in respect of the section 18 findings. My reasons are as follows. There is a very plain difference between the way the Tribunal reasoned in respect of the sex discrimination claim and the way it reasoned in respect of the pregnancy and maternity discrimination claim. The reasoning in respect of the sex discrimination claim involves a two-stage process entirely appropriate where the Tribunal is considering whether to find direct discrimination established in a case where the mental processes of the alleged discriminator are in issue. No such reasoning is found when the Tribunal considered the pregnancy and maternity discrimination claim. 33. This difference is particularly stark when the Tribunal considered the failure of Indigo to address the grievance of Mrs Martinez. The Tribunal found the very short period of delay at the outset to be maternity discrimination, without any reference to the burden of proof and despite acknowledging that the period was very short and not at all unusual. The Tribunal then adopted the conventional two-stage approach in determining whether the much longer period of delay amounted to sex discrimination. 34. The difference also appears to my mind from the use of the phrase "based on the premise that she is pregnant" in paragraphs 8 .1.1 and 84.2.1. The reasoning seems to be that, since a notification and risk assessment were required under statutory regulations to do with pregnancy or maternity leave, failure to provide them, or even in the case of the notification providing it a few days late, must be direct discrimination. This is not the law. Failure to provide a notification or a risk assessment relating to pregnancy or maternity leave may be, but is not necessarily, "because of" pregnancy or maternity leave. It may, for example, be a simple administrative error. The same process of reasoning is required in such a case as is required in any other discrimination case. 35. I have asked myself whether the Tribunal may have regarded the claims as falling within the first of the two categories which it identified in paragraph 14 of its Reasons. If so, it has misunderstood the approach in Amnesty International v JFS . The position is summarised on Onu which I have quoted. This is not a “criterion” case where TQIPS or Indigo applied the unfavourable treatment because of some rule or criterion which was inherently based on pregnancy or maternity. It is a case where the mental processes of the persons concerned fell to be considered. 36. To my mind, therefore, the reasoning concerning pregnancy and maternity discrimination cannot stand. The error of legal approach inevitable affects all the findings of pregnancy and maternity discrimination. Other findings appear to me to apply what is in effect a "but for" test and I notice also that, as regards failure to inform Mrs Martinez of the administration of TQIPS, the Tribunal set out no real reasoning at all on the question whether it was "because of" maternity. It follows that the findings of pregnancy and maternity discrimination must be set aside. 37. With those findings also I will set aside the determination of the Employment Tribunal that those claims were in time. The Tribunal's very brief reasoning in paragraph 85 will inevitably require to be revisited. For whether there was a course of conduct of a discriminatory nature will depend on findings which must be made applying the correct legal test. The reasoning of the Employment Tribunal is very brief. I do not say that I would necessarily have upheld the appeal relating to the time point on that ground alone, but when the question is revisited, some much more detailed reasoning would be valuable. It is, for example, not obvious from anything else in the Tribunal's reasons that Mr Tank was involved in all of the earlier aspects of the treatment involved. 38. As regards the finding of sex discrimination made in paragraphs 87 to 88, I reject the submissions of Mr Over. I do not accept that the Tribunal had in mind a wrong hypothetical comparator. The Tribunal referred itself to the fact that the male comparator was stating a grievance. It referred to the period concerned as "such period", that is to say a similar period to that which Mrs Martinez experienced. To my mind, there was no error of law so far as any hypothetical comparator is concerned. On the contrary, it seems to me that paragraphs 87 and 88 are a proper assessment of the sex discrimination aspect of the case made in accordance with the law. The failure by Indigo to address the position of Mrs Martinez seeking to return from maternity leave, ready, willing and able to work and taking positive steps to attempt to resolve the position through the grievance procedure was indeed remarkable. The Tribunal was entitled to find that the burden of proof shifted to the Respondent, and it was entitled to find the explanation lacking in cogency and credibility. The appeal concerning remedy issues 39. Mrs Martinez sought compensation for unlawful discrimination and unfair dismissal. I can deal briefly with two grounds of appeal concerning remedy. The Tribunal placed the award of compensation for injury to feelings at the top of the middle bracket applied in such cases. Mr Over sought to criticise this, but I see no error of law on the part of the Tribunal. The award for injury to feelings will need to be reconsidered if, on remission, the findings of pregnancy and maternity discrimination are changed, but in principle there was no error of law in the award of compensation for injury to feelings. 40. The Tribunal assessed an uplift of 15 per cent in respect of failure to follow the ACAS code of practice. Mr Over's Skeleton Argument and Notice of Appeal sought to argue that this was excessive, given the substantial commercial difficulties of TQIPS and Indigo at the time. I, however, see no error of law in the Tribunal's assessment, and Mr Over, I think, in fact withdrew this ground of appeal. 41. I now turn to Mr Over's principal ground, which requires more explanation. 42. The Tribunal made a modest award for psychiatric illness in the sum of £3,500. Mrs Martinez had in fact become depressed during 2011. There was a medical report concerning her condition from Dr Suleman, a consultant psychiatrist, dated 3 January 2013. Mrs Martinez was vulnerable to depression. Her vulnerability resulted from factors in her life long predating her work history. She suffered an episode of depression beginning in March 2011, which Dr Suleman found was caused in part by factors in her life which were not related to work, but also partly due to what he described as "work-related problems pertaining to the claim". As his report makes plain, he was aware of the nature of the claim which related to unpaid wages, sex discrimination in pregnancy and maternity discrimination and constructive unfair dismissal.43. He said that she was likely to recover from her current on-going depression within six months to one year. He said: "In my opinion, her work related problems pertaining to the claim have at least 50 per cent contributed to her current ongoing depression."44. The Tribunal in its findings accepted that the episode of depression began in March 2011 when Mrs Martinez learned that the Elsenham office was to close. It accepted Dr Suleman's opinion and awarded compensation for the episode of depression in the sum of £3,500. I should add that it carefully distinguished between the award for injury to feelings where it did not take account of Dr Suleman's report, and the award of compensation for psychiatric injury where it did.45. Mr Over argues that the tribunal was not entitled to accept Dr Suleman's report as a sufficient basis for an award of compensation for personal injury. Alternatively, he argues that the estimation of 50 per cent was inappropriate. He argues that there were "work-related issues" which were bound to occur in any event, such as the closure of the office. These did not follow from any unlawful discrimination. Further, he says, Dr Suleman's report took into account such matters as constructive unfair dismissal and wage deduction claims for which no award of personal injury could be made.46. In response to these submissions, Mr Hodson replies that the failure to inform Mrs Martinez properly of the closure of the office and most importantly the long drawn-out process which followed over many months were all the consequence of unlawful discrimination. Dr Suleman, by referring to "work related issues pertaining to the claim" plainly had in mind the complaints which Mrs Martinez was making rather than work generally. He submits that the constructive unfair dismissal claim and the claim for unpaid wages were extremely closely bound to the unlawful discrimination claim, such that an Employment Tribunal acting very much as a jury in respect of an award of general damages, was not obliged in law to separate them out. He further points out that Dr Suleman said the contribution was "at least" 50 per cent whereas the Employment Tribunal rounded the figure down to 50 per cent. Overall, he said, there was no error of law in the tribunal's reasons.47. On this part of the case, I prefer the submissions of Mr Hodson. It seems to me plain that Dr Suleman had in mind the complaints which Mrs Martinez was making. I do not, in the particular circumstances of this case, think that the Tribunal was required to make some further discount from Dr Suleman's assessment because he took into account constructive unfair dismissal or overdue wages. These were so closely bound up with Mrs Martinez's complaints that it would be unrealistic to do so. The award of £3,500 for the contribution which unlawful discrimination made to her depressive episode is moderate and I do not think it is vitiated by any error of law.48. The only point that I would make as regards the awards for personal injury and injury to feelings is that they would have to be reconsidered if on remission there are more limited or no findings of discrimination on grounds of pregnancy or maternity.49. I have dealt with Mr Over's main submissions but I should mention two other matters which are raised in the Notice of Appeal. In its Liability Judgment, the Employment Tribunal had declined to make any allowance under what is generally known as the Polkey doctrine. In paragraph 96 it said the following: “Next we deal with some points regarding Polkey contribution and the ACAS Code. With regard to Polkey , we find it difficult to see how Polkey could be said to have any application in this case. The principals [sic] are, that where a Tribunal finds that a dismissal was procedurally unfair, it should ask itself what percentage chance there is that a fair dismissal would have followed if a fair procedure had been followed. This is not a case of procedural unfairness, it is a case of constructive dismissal for the way that the Claimant had been treated. It seems to us that Polkey has no application in these circumstances.”50. This was a ground of appeal against the Liability Judgment. There would have been force in it. Even if a dismissal is constructive a Tribunal may have to consider whether and to what extent an employee would have remained in employment. This assessment, usually described in the context of unfair dismissal as a Polkey assessment, does not necessarily depend on the question whether the dismissal is constructive or actual.51. In its Remedies Judgment, however, the Employment Tribunal did not award compensation for loss of earnings for unfair dismissal. Rather it awarded loss of earnings for unlawful discrimination. When it did so, the Employment Tribunal did take into account what would have happened but for the discrimination: see paragraphs 41 and 42 of its Remedy Reasons. It recognised that Mrs Martinez might well have been made redundant and might have been out of work even if there had not been any discrimination. It concluded, however, that she would in any event have been at a disadvantage by reason of the discrimination because the discrimination was a cause of her depression which rendered her unfit to work. It took this into account and awarded loss of earnings until she was sufficiently fit to look for work, then scaling that loss of earnings down by 50 per cent to make allowance for the fact that she would, to some extent, have been depressed in any event.52. In these circumstances, the Polkey ground is of no further significance. The Tribunal did not make an award of compensation for unfair dismissal and, when it did make its award for discrimination, it took into account and estimated what would have happened but for the discrimination. This was the correct approach.53. Finally I should mention that there was a ground of appeal concerning comments which the tribunal made suggesting that the claimant may have lost an opportunity of transfer to Fujitsu. It is argued by these grounds that Mrs Martinez had no real prospect of any such transfer. However, in the event, as I have said, the Tribunal's award of compensation was not made on the basis that there was or would have been a transfer to Fujitsu.54. This brings me to the disposal of the appeal. I have found that the Tribunal's approach to the question of pregnancy and maternity discrimination was wrong in law. On behalf of Mrs Martinez, Mr Hodson submits that I am in a position to substitute my own conclusion to the effect that, even applying the correct test, the finding was bound to stand. I do not regard myself as in a position to reach such a conclusion. The Appeal Tribunal deals only with questions of law. It must remit a matter to the Tribunal for reconsideration unless, on a proper approach to the law, the Tribunal's finding is inevitable: see recently, Jafri v Lincoln College [2014] IRLR 544 . I do not think that can be said in this case.55. The question then arises whether remission should be to the same or to a differently constituted tribunal. Such a decision is taken by the Employment Appeal Tribunal in the light of guidelines set out in Sinclair Roche & Temperley v Heard [2004] IRLR 763 . I have given anxious consideration to those guidelines. I have reached the conclusion that it is appropriate to remit the matter to the same Tribunal. Although the Tribunal approached the matter incorrectly in law, I think it did so out of a misunderstanding of the boundary between the two types of "grounds" explained in Onu . I have every confidence that when the matter is remitted, it will apply the law correctly.56. The Tribunal's willingness to do so and to reach careful findings is fortified, in my view, by the fact that in paragraph 84.4.2 it expressed itself as willing to see the possibility that some complaint might be to do with communications failings rather than discrimination. It is plainly sensible and convenient that what is a relatively small part of the case should be remitted to the same Tribunal if at all possible. I have reached the conclusion that it is possible. Remission will be to the same Tribunal.57. I make it clear that the Tribunal should reconsider the question of pregnancy and maternity discrimination in all its aspects. It should start with the question whether there is unfavourable treatment. It should be prepared to listen again to submissions on that issue. It should then consider entirely afresh the "because of" question, again listening to submissions on that issue.58. Speaking for myself, I do not see the need for any further evidence to be called to the Tribunal. It should, however, as I have said, listen to further submissions and approach the pregnancy and maternity discrimination issues entirely afresh. Postscript. I am adding this postscript to the transcript of the judgment, which has been placed before me for correction and approval in August 2014. Very shortly after the argument and judgment in this case the previously unreported decision in Commissioner of Police of the Metropolis v Keohane was reported at [2014] Eq LR 386 . In that case the citation of authority, and the discussion of the principles concerning direct discrimination under section 18, was much wider than in this appeal; and the whole of the judgment of Langstaff P, but especially paragraphs 22-40, repays study. I draw this authority to the attention of the parties and the Employment Tribunal on remission. I believe, however, that the judgment which I have given adopts essentially the same approach. The true question for the Employment Tribunal to address is the “reason why” question.