DAVID Cameron has egg on his face, insisted Labour, after the Prime Minister made a diplomatic gaffe in front of the Queen by boasting how some “fantastically corrupt” countries would be attending this week’s anti-corruption summit in London.

The Prime Minister singled out Nigeria and Afghanistan, which are due to attend tomorrow's gathering hosted by the UK Government, as "possibly the two most corrupt countries in the world"

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The Opposition likened the diplomatic faux pas to that in 2014 when, in a conversation with Michael Bloomberg, the former mayor of New York, Mr Cameron was overheard saying how Her Majesty “purred” when he told her Scotland had voted against independence. Mr Cameron later apologised, saying he was extremely embarrassed by the incident.

This time, the PM made his controversial comments as he chatted with the Queen, the Archbishop of Canterbury and Commons Speaker John Bercow at a Buckingham Palace event to mark the monarch's 90th birthday.

Downing Street was quick to downplay the significance of the remarks, pointing out that the leaders of both countries had themselves acknowledged the scale of the corruption problem they faced.

But Labour’s Wes Streeting said: "This is another gaffe from the PM; you'd hope he'd have learned his lesson when it comes to off the record comments and the Queen; but sadly not.”

The London MP went on: "The fact that David Cameron has egg on his face shouldn't deflect from the more serious issue; for all his talk about corruption he's failing to act.”

He added: "If the PM really is serious about tackling corruption at the summit this week he needs to get his own house in order and make good on his promise to deliver public registers of beneficial ownership for the UK crown dependencies and overseas territories."

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During the filmed conversation at Buckingham Palace, Mr Cameron said: “We've got some leaders of some fantastically corrupt countries coming to Britain...Nigeria and Afghanistan, possibly the two most corrupt countries in the world."

The Archbishop, the Most Rev Justin Welby, was heard to intervene, saying "this particular president" was not himself corrupt.

Mr Bercow was also heard making a joke about the summit, quipping: "They are coming at their own expense, one assumes?"

After some laughter, Mr Cameron answered: "Yes...because it's an anti-corruption summit everything has to be open, so there are no sort of closed-door sessions; it's all in front of the press.”

He added: "It could be quite interesting but anyway..."

Asked whether the PM regretted his comment, a Downing Street spokesman said: "Both leaders have been invited to the summit because they are driving the fight against corruption in their countries. The UK stands shoulder to shoulder with them as they do so."

He declined to say whether the Nigerian or Afghan governments had contacted No 10 following Mr Cameron's remarks.

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The spokesman made clear the PM was aware he was being filmed at the time he spoke, telling reporters: "The cameras were very close to him. There were multiple cameras in the room."

Anti-corruption movement Transparency International ranked Afghanistan as 166th and Nigeria 136th out of 168 countries and territories in its Corruption Perceptions Index for 2015.