"If a client could sue his lawyer for negligence in conducting his litigation, he would have to prove not only that the lawyer has been negligence but also that his negligence had an adverse effect upon the outcome. This would usually mean proving that he would have won a case which he lost. But this gives rise to the possibility of apparently conflicting judgment which could bring the administration of justice into disrepute. A client is convicted and sent to prison. His appeal is dismissed. In prison, he sues his lawyer for negligence. The lawyer's defence is that he was not negligent but that, in any case, the client has suffered no injustice because whatever the lawyer did would not have secured an acquittal. In seeking to establish the latter point, the lawyer may or may not be able to re-assemble the witnesses who gave evidence for the prosecution. The question of whether the client should have been acquitted is then tried on evidence which is bound in some respects to be different, before a different tribunal and in the absence of the prosecution. The civil court finds, on a balance of probability, that the lawyer was negligent and that if he had conducted the defence with reasonable skill, the client would have been acquitted. Or perhaps that he would have had a 50% chance of being acquitted. Damages are awarded. But what happens then? Does the client remain in prison, despite the fact that a judge has said there was an even chance that he would have been acquitted? Should he be released, notwithstanding that the prosecution has had no opportunity to say that his conviction was correct? Should it be referred back to the Court of Appeal and what happens if the Court of Appeal, on the material before it, takes a different view from the civil judge? The public would not understand what was happening. So it was said that to allow clients to sue for negligence would allow a "collateral challenge" to a previous decision of another court. Even though the parties were different, this would be contrary to the public interest."