As an ex-military civilian I am horrified at the treatment that these people have been treated. I have done numerous postings and detachments in the service and also as a civilian.
There is no way a civilian organisation would DARE reduce an employees allowances once he has started an overseas position. To do so would be a flagrant breach of contract.
I would; on leaving the service if it was within seven years; sue the MOD for all the allowances that your litigation lawyer has assessed that you were due for, plus the legal expenses, plus personal and costs and stresses whilst on the posting.
Even the MOD is not above the law.