Britain's new Labour leader, Jeremy Corbyn, refused to sing the national anthem at a memorial service to remember the heroes of the Battle of Britain.
Mr Corbyn, a committed pacifist and republican, stood silently as the congregation at St Paul's Cathedral sang God Save the Queen on the aerial conflict's 75th anniversary.
Mr Corbyn, who was dressed in non-matching jacket and trousers and had failed to properly button his shirt, was branded a "disgrace" by critics.
His spokesman defended his actions, saying Mr Corbyn had attended the service "to show respect for those who fought" for Britain, but confirmed he had not sung the anthem on purpose. A Labour source added: "He stood in respectful silence during the anthem."
David Cameron, who attended the event alongside Mr Corbyn and a host of other dignitaries and Royals, aimed a thinly-veil barb at the Labour leader for failing to sing the anthem.
The Prime Minister's official spokeswoman said: "The importance the Prime Minister attaches to the national anthem is well known. Every time he is at one of these commemorative services he is very proud and willing to join with others in singing the national anthem."
Ahead of the memorial service Mr Corbyn also met Mr Cameron for the first time since his victory - hours after he was embroiled in a major row with his own MPs after refusing to say if he will wear a red poppy on Remembrance Sunday because he is a pacifist.
Earlier Mr Corbyn did pay tribute to the "heroism" of the Royal Air Force but wants to prevent future military action.
He 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.
- Dail Mail