"In considering the approach to be taken by this court to the decision of the judge, it was rightly accepted by Aspinwall that the decision to be made is not the exercise of a discretion; WSP were wrong in contending otherwise. It was a decision involving the assessment of a large number of factors to which there can, in such a case, only be one correct answer to whether there is or is not an abuse of process. Nonetheless an appellate court will be reluctant to interfere with the decision of the judge where the decision rests upon balancing such a number of factors; see the discussion in Assicurazioni Generali v Arab Insurance Group[2002] EWCA Civ 1642 , [2003]1 WLR 577 and the cases cited in that decision and Mersey Care NHS Trust v Ackroyd[2007] EWCA Civ 101 at paragraph 35. The types of case where a judge has to balance factors are very varied and the judgments of the courts as to the tests to be applied are expressed in different terms. However, it is sufficient for the purposes of this appeal to state that an appellate court will be reluctant to interfere with the decision of the judge in the judgment he reaches on abuse of process by the balance of the factors; it will generally only interfere where the judge has taken into account immaterial factors, omitted to take account of material factors, erred in principle or come to a conclusion that was impermissible or not open to him. In this case, I consider that the judge, despite the weight that must be accorded his view given his great experience in this type of litigation and the conspicuous success with which he has managed the TCC, reached a decision which was impermissible by taking into account factors which he should not have done and omitting factors which he should have taken into account."