I believe the reason for the use of civil licensed engineers is most probably because the aircraft is also civil certified. For it to have a resale value it has to be maintained to civil standards.
This is not uncommon with a number of aircraft being maintained in this way e.g Bell 412, Agusta AW 139 and others. The MOD is trying to protect the tax payers investment rather than see aircraft sold for scrap value at the end of their military careers.
From a maintenance engineers point of view good news with salaries on offer of over £45k.
That can be compared with the appalling low rates of pay offered on other military contracts and indeed to military personnel. Elsewhere on this forum I believe the starting pay for an RAF aircraft technician was quoted as being £17,000. Less than a PTI or a military policeman. Maybe the penny will drop and we will see a decent pay rise for military aircraft technicians.
I can only see the exodus to civvy street of experienced staff continuing.