If you leave the Military and say join the Civil Service, you can transfer your Military pension, into the Civil Service Pension Scheme, but it WILL NOT be on a like for like transfer.
I suspect this relates to pension earned rather than pension received. Ie if you had earned 12 years in the military then that service would count towards the civil service pension but supposing the civil service pension is based on 80ths whereas the military is based on 60ths then this would only benefit the CS pension to 12x3/4 or 8 years. That is just speculation but I think you can see why it might be true.