"So my own suspicion is that the attorney has stopped this prosecution because part of her defence was to question legality and that would have brought his advice into the public domain again and there was something fishy about the way in which he said war was legal"

Clare Short is suggesting that the lawyer has stopped the prosecution due to the fact that the defence was questioning the legality of the scenario. This would have brought the attorney's guidance into the general public domain, which might have revealed something suspicious about the way in which he said war was legal. This implies that the lawyer was aware of something that might have been harming to his credibility, therefore he picked to end the prosecution in order to avoid additional analysis. It is possible that the attorney was aware of something that could have been seen as dishonest or prohibited, therefore he selected to end the prosecution in order to protect himself. This quote suggests that the lawyer was not acting in the very best interests of justice, but rather in his own self-interest.