Donald Trump's comments about Islamist radicalisation in London make him "unfit" to be US president, the city's mayor Boris Johnson has said.
The property tycoon and reality TV star, who is seeking the Republican nomination for next year's presidential election, has provoked widespread anger and ridicule after calling for a ban on Muslims entering the United States and claiming that parts of the British capital were "so radicalised" that police were "afraid for their own lives".
A petition calling for Mr Trump to be barred from entering Britain has received more than 200,000 signatures on the parliamentary website, meaning that it will be considered for debate in the House of Commons. At one point, the petition was lengthening by more than seven signatures a second.
But Chancellor George Osborne dismissed calls for Trump to be excluded from the UK, saying it was better for his "nonsense" views to be challenged in debate.
Downing Street has made clear that David Cameron regards the presidential hopeful's comments as "divisive, unhelpful and quite simply wrong".
But Mr Johnson is the first prominent British politician to suggest they render Mr Trump unfit for office.
The mayor told ITV News: "I think Donald Trump is clearly out of his mind if he thinks that's a sensible way to proceed. You can't ban people going to the US in that way, or indeed to any country.
"What he's doing is playing the game of the terrorists and those who seek to divide us. That is exactly the kind of reaction they hope to produce.
"When Donald Trump says there are parts of London that are no-go areas, I think he is betraying a quite stupefying ignorance that makes him frankly unfit to hold the office of the president of the United States."
Mr Johnson joked: "I would invite him to come and see the whole of London and take him round the city, except that I wouldn't want to expose Londoners to any unnecessary risk of meeting Donald Trump."
Challenged in the House of Commons over calls for a ban on Mr Trump entering the country, Mr Osborne said that the outspoken Republican was "profoundly wrong" about Muslims.
But he added:"I think the best way to defeat nonsense like this is to engage in robust, democratic debate and make it very clear his views are not welcome."
Any issue on which a petition exceeds six-figure support is expected to be debated by MPs unless it is deemed "unsuitable" by the Commons petitions committee - or is being pursued "in another way".
The committee is not due to meet again until January 5.
Downing Street said any question of a ban on Mr Trump coming to Britain was "hypothetical" as it was not aware of any plans for him to visit.
"I think we would probably see Mr Trump's focus as being on the American presidential election," said a Number 10 spokesman. "I understand he has a primary to fight in six weeks and I'm sure that is what his focus will be on."
Scottish First Minister Nicola Sturgeon stripped Mr Trump of his membership of the GlobalScot business network, saying that he was no longer fit to act as a business ambassador for Scotland.
More than 20,000 people have now signed a petition calling for him to be stripped of his honorary degree from Robert Gordon University (RGU) in Aberdeen, where he was awarded a doctorate of business administration in October 2010.