that would be a Civilian RB as used by Utility companies, and as Fire engines, its Not Military, is it a V6 Ford engine ? what year is it? to be Historic Exempt 40year old it has to be pre 1980. otherwise It will Not be ULEZ compliant, must be Euro 4 petrol, or pay £12.50 a day. but it can still be used ok outside of the ULEZ, which expands out to the North & South circular roads in October this year