Anti-war campaigner Jeremy Corbyn called for politicians to do everything possible to spare future generations from the "horrors of war" as he arrived at Battle of Britain commemorations.
Labour's new leader attended the service at St Paul's Cathedral as he was embroiled in a row over his pacifism after refusing to rule out wearing a white poppy on Remembrance Sunday.
Dressed in non-matching jacket and trousers with a blue shirt and maroon tie, Mr Corbyn paid tribute to the "heroism" of the Royal Air Force but called for action to prevent future military action.
The Stop the War Coalition chairman said: "My mum served as an air raid warden and my dad in the Home Guard.
"Like that whole generation, they showed tremendous courage and determination to defeat fascism. The heroism of the Royal Air Force in the Battle of Britain is something to which we all owe an enormous debt of gratitude.
"The loss of life - both civilian and military - should be commemorated so that we both honour their lives and do all that we can to ensure future generations are spared the horrors of war."
The leader of the opposition is thought to have arrived on foot around 15 minutes before the St Paul's Cathedral event, attended by veterans, their families and senior RAF officers, began.
Mr Corbyn took his front-row seat briefly, before standing to talk to some of the other guests.
David Cameron arrived sometime later and sat down at the end of a row a few seats away from the Labour leader.