“75. A failure to see that a claimant was adequately informed before service of a notice under regulation 4 would be likely to, but would not necessarily, vitiate the service of the notice. That would depend on whether the failure was material. Public law is flexible in dealing with the effects of procedural failures. Ultimately the issue must be determined by reference to the justice of the particular case. If the effect of the lack of information given to a claimant materially affected him or her by removing the opportunity of making representations which could have led to a different outcome, it would normally be unjust to allow the notice to stand. If it was immaterial on the facts, justice would not require the notice to be set aside.”