The Post Retirement Marriage rule (which applies in many 'old' pension schemes) has been challenged over the years and has been upheld as legal. Debate on this and other AFPS 75 'legacy issues' took place during the passage of the Armed Forces (Pensions and Compensation) Act 2004 through Parliament and that did not result in a retrospective change. I am not aware of any new challenge and, given the firm 'non-retrospection' policy, I would not expect success if there were to be a challenge.