Prince congratulates Boris ... but there's no word from Gordon yet

Prince Charles's "warm" regards, in a handwritten letter to Mr Johnson, contrast with the Prime Minister's failure to contact him 11 days after his victory.

The heir to the throne, who shared the Henley MP's opposition to the foxhunting ban, is the most senior figure to get in touch following the defeat of Ken Livingstone on 1 May.

Communities Secretary Hazel Blears, who has responsibility for local government, telephoned the new Mayor and he has received a "gracious" handwritten letter from another senior minister.

Olympics minister Tessa Jowell will meet Mr Johnson formally for the first time tomorrow when the pair discuss the plans for the 2012 Games in the capital. Overseas figures have also sent their congratulations, with New York mayor Michael Bloomberg one of the first to call on election night.

But in an echo of his refusal to congratulate SNP leader Alex Salmond until long after his election as First Minister of Scotland last year, Mr Brown has yet to call the Mayor.

Mr Johnson said Mr Brown's frostiness was at odds with the approach of Londoners he meets around the city, with even those who did not vote for him offering their best wishes.

Mr Johnson said that he was "not surprised" that the premier had failed to get in touch because he had heard that Mr Brown had been "gutted at the grievous loss" of London to the Conservatives. Claiming that Number 10 was now copying Tory policies just as Mr Livingstone had sought to steal his own ideas, Mr Johnson joked: "Brown is bobbing in our wake like a cork."

One City Hall source said: "It's becoming embarrassing now. When is Gordon going to swallow his pride, do the honourable thing and make the call?"

The Prince's intervention underlines his keen interest in politics and his affection for Mr Johnson. His letter is understood to refer to the importance of the office of Mayor of London.

Mr Brown's behaviour is sure to be seized on by Tories as proof of his "character" problems and comes amid a war of words within Labour over his personality. Labour MP Frank Field came under fire from Education Secretary Ed Balls yesterday for attacking the Prime Minister, and No 10 was forced to deny Cherie Blair's suggestion that Mr Brown may have leaked news of her pregnancy with Leo.

Former deputy prime minister John Prescott also referred in a new memoir to Mr Brown being "prickly" and frequently in a bad mood over his poor relations with Tony Blair.

Downing Street said Mr Brown had congratulated Mr Johnson publicly, including in the Commons and in TV interviews. A spokesman said Mr Brown would make contact with the Mayor "when they have matters to discuss".

However, when the Mayor appeared at Prime Minister's Questions last week, Mr Brown stopped short of congratulating him and merely said that he welcomed his appearance in the Commons.

It took Mr Brown four weeks to telephone Mr Salmond with his congratulations after the Scottish Parliamentary elections last summer.