Charles put an 'urgent call' into ambassador William Farish (right) urging the U.S. to halt the invasion

Prince Charles tried to halt the American invasion of Afghanistan to ‘honour’ Ramadan.

He made the plea to the US ambassador to London four weeks into the huge military operation launched after the 9/11 terror attacks.

The startled envoy asked the prince, ‘Sir, are you really serious?’ according to a book being serialised from today by the Daily Mail. Charles’s intervention appears to have been made behind the back of then prime minister Tony Blair.

Last night an officer who led UK forces in Afghanistan said the prince’s request was absurd. Critics described it as grossly irresponsible. Politicians in the UK are used to the prince trying to meddle in policy and his handwritten ‘black spider memos’ are legendary.

Twenty thousand American and British troops were ordered to Afghanistan by George W Bush and Mr Blair in October 2001 because the ruling Taliban had refused to give up Al Qaeda leader Osama Bin Laden.

Around a month into the offensive – and two weeks before the start of the Muslim holy month of Ramadan – Charles placed an ‘urgent call’ to William Farish, Washington’s ambassador to London.

Interviewed for the new biography of Charles, Mr Farish recalled: ‘Prince Charles asked me if it would be possible to stop the invasion to honour Ramadan, and if I could convey that request to President Bush.’

While British politicians have gotten used to Charles' attempted meddling, the U.S. envoy was shocked by the prince's request

In the days after the 9/11 attacks Tony Blair pledged to stand shoulder to shoulder with U.S. President George W. Bush

The ambassador explained it would be rather difficult to halt a military invasion already in full swing, but the prince allegedly protested: ‘But Americans can do anything!’

The envoy asked: ‘Sir, are you really serious?’ and the heir to the throne replied, ‘Yes I am’.

The extraordinary exchange is revealed in Prince Charles: The Passions And Paradoxes Of An Improbable Life by Sally Bedell Smith. The respected historian based the biography on interviews with more than 300 friends, family and associates of the prince.

Three days after the 9/11 attacks, Charles, the Queen and Mr Blair stood shoulder to shoulder with Americans including Mr Farish at St Paul’s Cathedral for a service of remembrance.

The invasion was launched less than a month later on October 7, with Mr Blair declaring that ‘the stability of the world’ depended on it.

Yet at the start of November the prince was allegedly trying to thwart government policy.

Twenty thousand British and American troops invaded Afghanistan in 2001 when the Taliban refused to hand over Osama Bin Laden

‘I am somewhat surprised that Prince Charles should attempt to get involved in a military operation,’ said Colonel Richard Kemp, who subsequently commanded British forces in Afghanistan.

‘Obviously that is not what he is there for.

‘He shouldn’t have attempted to interfere at all, and let alone on the basis of Ramadan.

‘If anything, a military commander should exploit opportunities like Ramadan rather than be controlled by a religious festival. It shows a surprising lack of judgment, that he felt it was his place to meddle like that, and the idea that on the basis of Prince Charles’s personal opinion, the UK would dictate American military operations is just absurd. There was no option. Afghanistan was harbouring terrorists who had launched a devastating attack on the US. Who was Prince Charles to intervene?’

Colonel Richard Kemp said that a competent military commander 'should exploit opportunities like Ramadan rather then be controlled by a religious festival'

Graham Smith, of the anti-monarchy campaign group Republic, said: ‘How can we tolerate a future head of state who behaves in such an irresponsible unprofessional manner?

‘This is one of the most serious cases of royal meddling that’s come to light. It is grossly irresponsible to be interfering in such a serious and delicate situation and in one of the UK’s most important international relationships.

‘People will have strong feelings about the invasion, but none of the controversy justifies Charles’s interference. He must be told to back off.

‘We elect a government to handle our international relationships. Charles’s unwanted intervention only risks damaging our reputation and relationships with our allies.’

Mrs Bedell Smith recalls that US defence secretary Donald Rumsfeld had noted that Muslims themselves waged war in the holy month – Iran and Iraq eight times during their conflict in the 1980s, and Egyptian president Anwar Sadat in his 1973 attack on Israel. She said Mr Rumsfeld added: ‘The Taliban and Al Qaeda are unlikely to take a holiday.’

The book also claims that Prince Charles tried to influence Margaret Thatcher - which led to an irate call from Downing Street where Mrs Thatcher said: 'I run this country, not you sir'

Now back in America, Mr Farish, 78, was unavailable for comment last night.

The book also claims that Charles tried in vain to influence Margaret Thatcher.

The confrontation came in 1985, when the prince was fretting that Tory policies meant he would ‘inherit the throne of a divided Britain’.

The prime minister was ‘so incensed she called Buckingham Palace to complain’ demanding to know what was going on. Charles was said to be flabbergasted that Mrs Thatcher could tell him: ‘I run this country, not you, sir.’