Indeed. In this instance my advice would be to tell them what you've done, if you want to try and obtain an out of court settlement.Or indeed, as in the case in question, the letter received specifically said that they have already audited your purchases and mentions "other occasions" where they believe you have done the same thing. In which case I would suggest it is extremely inadvisable to stay silent, where you know they have a sure fire case against you for the one offence.