Boris Johnson has dismissed critics of Donald Trump as “puffed up pompous popinjays”, hours after the US president cancelled a visit to London to open the new American embassy.
The Foreign Secretary said people who welcomed news the US leader would not visit Britain were “determined to put” a “crucial relationship at risk”.
The announcement by Mr Trump sparked mixed reaction.
London mayor Sadiq Khan said Mr Trump had “got the message” that people in the capital “find his policies and actions the polar opposite of our city’s values”.
But Mr Johnson tweeted: “The US is the biggest single investor in the UK – yet Khan & Corbyn seem determined to put this crucial relationship at risk. We will not allow US-UK relations to be endangered by some puffed up pompous popinjay in City Hall.”
A popinjay is a type of parrot, sometimes used as an insult to describe someone vain or who behaves extravagantly.
Labour leader Jeremy Corbyn has not publicly commented on Mr Trump’s cancelled visit.
Downing Street later said the “strong and deep” partnership between Britain and the US “will endure”.
Asked if the Prime Minister shared the President’s view of south London, Theresa May’s spokesman replied: “It is a vibrant and important part of London, home to many businesses.”
A Number 10 source told Sky News: “Boris expresses himself in his own inimitable way – but we agree that any risk to the crucial US-UK relationship is not in our country’s best interests.”
Local Labour MP Marsha De Cordova told Sky News she was “pleased” Mr Trump would not be travelling to the UK because he was “really scared” of being met by a peaceful protest made up of hundreds of thousands of people.
Mr Trump had been expected to visit the new £750m ($1bn) home for American diplomats on the banks of the River Thames as early as next month.
The new Nine Elms site, near Battersea in London, is due to open on 16 January.
Mr Trump’s announcement came in a tweet posted just before midnight local time (5am GMT).
He wrote: “Reason I cancelled my trip to London is that I am not a big fan of the Obama Administration having sold perhaps the best located and finest embassy in London for ‘peanuts,’ only to build a new one in an off location for 1.2 billion dollars. Bad deal. Wanted me to cut ribbon-NO.”
Despite Mr Trump blaming his predecessor for moving the embassy from Grosvenor Square, its home for 80 years, the move was actually initiated by the George W Bush administration.
A post on the embassy’s website dated 8 October 2008 – just under a month before Mr Obama’s election – revealed the plan.
It said: “The US State Department today signed a conditional agreement with the real estate developer Ballymore to acquire a site in the Nine Elms Opportunity Area in Wandsworth for the construction of a new Embassy.”