New Labour Party leaders Jeremy Corbyn and John McDonnell were last night sensationally accused of risking inciting terrorist and anti-Semitic attacks in London.

The claim was made by the Labour candidate for London Mayor, Sadiq Khan, in a devastating assault on Corbyn and the man he has made Shadow Chancellor.

Khan, who is Muslim, suggested that Corbyn's refusal to sing the National Anthem showed he was unfit to be Prime Minister.

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'I'll be my own man': Sadiq Khan, Labour candidate for London Mayor, in his Tooting constituency last week

And he denounced the Labour leadership duo's links to terror groups. He said McDonnell's claim that IRA killers should be 'honoured' could encourage terrorism in London, and Corbyn's support for Arab extremist groups could inspire anti-Semitic attacks.

Khan's comments were echoed by fellow Labour MP Chuka Umunna, whose Streatham constituency includes Brixton, hit by riots in the 1980s.

Umunna said Corbyn's leadership could leave Labour out of power for years and trigger a repeat of the 'Tory injustice' of the Thatcher era which had 'boiled over' in the Brixton riots. Asked if he meant it could spark violent unrest, Umunna said: 'I wouldn't dismiss it.'

Khan said anyone aspiring to be Prime Minister should sing the Anthem. He said he sang it regularly and spoke with pride of kissing the Queen's hand when he was made a Privy Counsellor in a ceremony the Labour leader is threatening to boycott. His comments are all the more pointed given his Pakistani roots.

Claims: New Labour Party leaders Jeremy Corbyn (left) and John McDonnell (right) were last night sensationally accused of risking inciting terrorist and anti-Semitic attacks in London by Khan

Khan said: 'My family has always been proud of being British. My cousins in Pakistan say, 'You are one of the Queen's advisers'.'

Corbyn was 'very unwise and disrespectful' to refuse to sing the Anthem at last week's Battle of Britain memorial service.

Asked if he could stomach McDonnell's comment about 'honouring' IRA terrorists, Khan said: 'No. You cannot condone terrorism. You are giving credibility to a view that is perverse and that is wrong.'

It was 'particularly dangerous' in London, which had been the target of IRA and militant Islamist outrages. Khan also backed claims that Corbyn's links with Palestinian terror groups could fuel anti-Semitism in the UK.

Corbyn (right) stands silent as the national anthem is sung during a service at St Paul's Cathedral in London

Asked to comment on Corbyn's Hamas and Hezbollah connections, he said Labour had to ditch its 'anti-Jewish' image, which was not acceptable' in Britain.

Khan said there was a direct link between Middle East tension and anti-Semitic attacks in London, saying synagogues and Jewish schools in London needed 24-hour guards as a result.

Khan also disowned Corbyn's and McDonnell's policies including a 'ridiculous' 60p top tax rate, scrapping nuclear weapons, leaving Nato and nationalising banks, and said he would not take orders from Corbyn if he became mayor. 'I will be my own man,' he vowed.

Corbyn was very unwise. You want to be PM? Respect our Queen - and sing the Anthem

Sadiq Khan still chuckles at the memory of the day in 2009 when he joined the Privy Council at Buckingham Palace.

Two weeks earlier Gordon Brown had invited Khan to attend Cabinet meetings, adding gruffly, 'you're a PC' – and leaving Khan bemused.

'I had no idea what it meant. I had to call No 10 and ask. They said, 'You're a Privy Counsellor, a Right Honourable'.'

'The Palace called me and said, 'What type of Bible do you want to swear on?'

'When I said the Koran, they said, 'We haven't got one'. So I took one with me.'

Crowned: Patriotic Khan, right, in 1977 at the Queen's Silver Jubilee party

Jeremy Corbyn may despise the arcane ritual whereby new Privy Counsellors get down on one knee before the Monarch.

Khan did it so enthusiastically that Speaker John Bercow, also made a 'PC' that day, has never let him forget it.

'You go into a room, the Quee… Her Majesty is there,' says Khan, 44, correcting himself deferentially.

'You go down on one knee on this little stool… It's so amazing, it moves you. Her Majesty puts her hand out. I held the Koran with my left hand. You touch your nose against her hand. Then I kissed her hand,' he smiles, recalling his faux pas.

'You aren't supposed to kiss her. You're just supposed to brush her hand with your nose.' He acts it out with his own nose on his hand.

'Bercow still teases me about it. As I was leaving this, er, woman...'

A Lady in Waiting? I ask.

Eight months from now, the Rt Hon Sadiq Khan MP PC could be Labour's most powerful politician in Britain

'Yeah, this Lady in Waiting said, 'Here is your Koran, Mr Khan'. I said, 'Leave it for the next person'.'

Eight months from now, the Rt Hon Sadiq Khan MP PC, the Labour candidate for London Mayor, could be the party's most powerful politician in Britain.

The son of Pakistani immigrants, his father was a bus driver and his mother a seamstress.

Khan, who is married to fellow lawyer Saadiya and who has two teenage daughters, grew up in a tiny council flat in Tooting, South London, where he is now MP, with six brothers and one sister.

A sense of patriotism was drummed into them.

'We have photos of us going on family day trips to Buckingham Palace,' he says as we chat in the Tartine café in his Tooting constituency.

Whenever there is tension in Middle East it leads to anti-Semitism in our country. There are Jewish schools and synagogues in London which need round-the-clock security. I will have a zero-tolerance of anti-Semitism Sadiq Khan

'My family's always been proud of being British. When Pakistan beat England at cricket my Pakistani cousins remind me how English and British I am. When they say, 'You're one of the Queen's advisers', for them it's 'Wow – anything's possible in the UK'.'

He has no time for Corbyn's refusal to sing the National Anthem at the Battle of Britain memorial service.

'He was very unwise. You are trying to be the British Prime Minister: you should be singing the National Anthem. It was a mistake, especially on that occasion. You have to show respect. You may have strong views about the National Anthem. But you want to be the British PM? It was the Battle of Britain commemoration,' he repeats with an exasperated 'for heaven's sake' tone. You won't catch Khan tight-lipped when the Anthem strikes up. 'I sang it at Tooting Methodist Church a few weeks ago,' he says cheerily.

If Corbyn wants to see patriotism in action he should go to a town hall citizenship ceremony and hear new immigrants sing it, suggests Khan: 'They're so proud, they know all the verses!'

He is equally critical of Corbyn's links with Palestinian terror groups such as Hamas and Hezbollah, claiming they reinforce 'the perception at the last Election that Labour is anti-Jewish.

'Whenever there is tension in Middle East it leads to anti-Semitism in our country. There are Jewish schools and synagogues in London which need round-the-clock security. I will have a zero-tolerance of anti- Semitism – it's not acceptable in 21st Century London.'

Khan gives short shrift to Corbyn's ally and Shadow Chancellor John McDonnell and his talk of 'honouring' IRA terrorists.

Congratulations: Khan MP (centre) is congratulated by his supporters at the Royal Festival Hall, London, after it was announced that he has been chosen as the Labour candidate to run for London mayor in 2016

'The idea that a senior politician can condone terrorism is not me,' he frowns.

'Language is very important. If you are condoning acts of terror… you are giving credibility to a view that is perverse and is wrong.' Could it encourage others to commit similar acts?

'You're condoning when you should be unequivocally condemning criminal acts, yes.'

It was 'particularly dangerous' in London which had been hit by IRA and Islamist terrorists.

'As Mayor I'll make sure we don't inadvertently give the signal that it somehow leads to good results. You can't do that.'

His likely opponent in the mayoral election next May is multi-millionaire Tory poster boy Zac Goldsmith.

They will make an odd couple at the hustings: at 6ft 3in tall, blue-blooded Goldsmith is a good nine inches taller than 'sarf Londoner' Khan.

'If it's a referendum on who is best looking I may not win. But I learned a long time ago size isn't everything,' he quips.

If it's a referendum on who is best looking I may not win. But I learned a long time ago size isn't everything Khan

Khan is not just a political street fighter. He learned to box at the local Earlsfield Boxing Club where a certain Frank Bruno honed his skills.

He used his fists on the Henry Prince estate in Tooting, just round the corner from where we are sitting, as a young boy.

'People soon learned who they could pick on,' he says, chin jutting. He once got into a fight with a white boy who called him 'Paki'. Khan recalls: 'We went down on the floor hitting each other. He didn't call me the 'P' word again.'

He saw his father suffer similar abuse when, as a boy, Khan rode on the upstairs of his double decker bus. 'He had a beard and passengers would call him Paki Santa. He was assaulted – you don't forget things like that.'

Don't expect to see Corbyn centre-stage of Khan's mayoral campaign. He sniggers at Corbyn and McDonnell's outlandish views such as a 60p top tax rate and nationalising the banks – a matter of some interest to the Mayor of London.

'The idea that our banks would be viable when there's a sword of Damocles hanging over them from the Government is not realistic. By the way I gather it's without compensation!' he scoffs.

The 60p income tax rate is 'ridiculous', while Khan pledges 'passionate' support for Nato, the EU and Britain's nuclear deterrent – all on Left-winger Corbyn's hit list.

To add insult to injury, Khan says he is just as likely to take advice from David Cameron as Corbyn. 'I'll be my own man and work closely with a Tory Government if it is in London's interest,' he says.

Khan is slick, some would say too slick. A teetotal, union-backed supporter of gay marriage, when he decided to run for London Mayor he abandoned his support for a third runway at Heathrow quicker than a Concorde take-off.

Listening to him, you'd never believe he nominated Comrade Corbyn for leader: it won him enough Left-wing votes to see off 'uber-Blairite' Labour rival Tessa Jowell in the contest to be Mayor.