I hesitate to say it because I know from her posts that Ethel is normally very accurate, but I don't think she is right this time! If the tax which would have been paid if he had not gone bankrupt is kept by him, then he is financially in a better position - to the amount of that tax - by going bankrupt. My understanding of the position is that the NT tax code (which does not have to be requested by the bankrupt - it is done by the official receiver contacting inland revenue) is implemented so that the tax which would have been paid is given instead to the official receiver as a contrbution towards the costs of the bankruptcy.
Normally, the bankrupt is asked to sign an agreement to pay over to the OR each month the amount he has gained by not having tax deducted. I don't understand why your partner has not been sent such an agreement. My advice would be not to spend the money - keep it in an account in case it is asked for later - or go back to the OR again, tell him what has happened and ask for confirmation whether he can keep the money. (I don't think he'll get such confirmation!)
Incidentally, if the bankrupt changes jobs the NT tax code should be on the P45 & applied by the new employer.