Another discount added for those interested The Veterans Oyster card,
but please note,
If you have a War Pension (must be War not AFPS75 or any other military pension) then you can travel free off peak within TFL boundaries and anytime on buses and tubes with the ‘Veterans’ Oyster card (Not to be confused with the ‘Veteran’ Rail card.
Other train operators provide free/discounted travel on their routes too so please do check.
To apply you have to call 0330 124 3941 and ask for an application form to be sent through the post (yes this is still the 21st century!) See this link for full details.