If you think that HM will step in the way to protect Forces pensions in opposition to government decisions, think again.
EVERY law is signed by the queen, including changes to the UK constitution. If HM signed off the Lisbon treaty ammendments to the UK constitution, I cant imagine her raising her head above the parapet regarding pensions.
Whether we like it or not, Whitehall has to find 25% cuts in expenditure, current and future. One of the easiest ways of doing this is by ammending public sector pensions, which are currently unfunded and not in the future government debt statistics.
Have a look to see what they have done to redundancy terms if you think pensions are gold plated... the retrospection law will last as long as our government carries on without IMF bailout. Once we get past that little number again, all bets are off.