Inland revenue and tax....?

One thing that may help his case is if the money was paid into a bank account to which he has had no access since the split or ever. If it went into a joint account that he could still access, then it is unlikely the taxmen woudl believe him, though a full set of statements for the time in question, showing that he neither paid in nor withdrew funds might be helpful. I suppose there is no possibility of appealing to his former partner to say that she received all the money and he is not liable? There are some people out there with a conscience.