Labour has defended its new leader's refusal to sing the national anthem during a Battle of Britain commemoration - stressing he listened in "respectful silence".
Mr Corbyn - who has previously called for the monarchy to be abolished - kept quiet while David Cameron and others attending the service at St Paul's cathedral service sang God Save the Queen.
The event, on the 75th anniversary of the Battle of Britain, was honouring the "many" who supported the pilots famously described by Winston Churchill as "The Few".
Tory MP Sir Nicholas Soames, Churchill's grandson, said not singing the anthem was "very rude and very disrespectful" to the Queen and "the Battle of Britain pilots who gave their all". "It was an extremely disrespectful thing and I think he needs to make his mind up whether he is a grown-up or not," he said.
Fellow Conservative Andrew Rosindell, who has campaigned to promote patriotism, said it was "disappointing" Mr Corbyn had chosen not to sing.
"I congratulate Jeremy on his success and he is a man of principle, he has strongly held views and I respect him for that. However, I hope that now he is leader of Her Majesty's Opposition and leader of the Labour Party he will understand that the British people are overwhelmingly supportive of our monarchy and our constitution."
Ukip leader Nigel Farage, who was also at the service, described Mr Corbyn as a "hardcore republican".
"I was at St Paul's and noticed Jeremy Corbyn not uttering a world of the national anthem, but then he is a hardcore republican to his fingertips, something that very few Labour voters would support," he said.
Downing Street said Mr Cameron attached "importance" to the national anthem and was "very proud" to sing it. The Prime Minister's official spokeswoman said: "The importance that the PM attaches to the national anthem is visible every time he is at one of these commemorative services. He is very proud and willing to join with others singing the national anthem."
Ahead of the event, Mr Corbyn highlighted that his mother had served as an air raid warden and his father in the Home Guard.
He said: "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."
A spokesman for Mr Corbyn said later: "Jeremy attended today's event to show respect for those who fought in conflicts for Britain.
"As he said in the words issued this morning, the heroism of the Royal Air Force in the Battle of Britain is something to which we all owe an enormous debt of gratitude. He stood in respectful silence during the anthem."
Mr Corbyn, who is usually seen in and around Westminster casually dressed, wore a blue shirt, burgundy tie and mismatched dark jacket and trousers for the occasion. After the service, he said it had reminded him of his mother. Asked about attending St Paul's for his first major event as Labour leader, he said: "I've been there before - it's such a beautiful church.
"I was thinking of my mum. She was an air raid warden - I've got the ARP medal she was given."
Conservative James Gray, a member of the Defence Select Committee, said Mr Corbyn should be praised for attending the event.
He said: "The fact he was there properly dressed, wearing a tie, good on him. Well done him.
"He is a pacifist and not a royalist but he has gone along and stood in the front row."