There are very good reasons for not allowing personal use of military vehicles, mostly tax. If a vehicle is kept at a business address and is used for business to business travel only (there are small allowances for journies via home such as picking up kit etc) then the MOD can claim all of the VAT back from the vehicle purchase/hire and the fuel. Otherwise it becomes 50% and depending on the vehicle that can be a considerable amount. Hence the rules. Also by putting in his own fuel he will have prevented the bean-counters from being able to calculate personal/professional usage ratio and thus would probably had to forfeit the entire VAT amount to HMRC. Being warned and subsequently ignoring them basically meant he was digging a trench to bury his career in. Fool.