Organisers of an anti-Trump campaign have warned more than a million demonstrators could take to the streets if the President’s proposed visit to the UK goes ahead early next year.

Following a furious backlash against Donald Trump after he retweeted anti-Muslim videos shared by far-right group Britain first, organisers of the Stop Trump group claim to have seen an avalanche of pledges to protest in the event any such visit.

“We’ve had a huge response to our campaign over the last 24 hours – particularly on social media,” a spokesman told the Evening Standard.

“Thousands of people have been signing our pledge to protest.

“The British government know that the protests against a Trump visit could be the biggest we’ve ever seen in the country. Upwards of a million people could take to the streets.

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“No doubt that’s a factor not only in the delay over the visit but also the secrecy surrounding the details.

“But there’s no escape. We could mobilise hundreds of thousands at a day’s notice.”

The Stop Trump group formed in February in response to the President’s short-lived and highly controversial “travel ban” against residents of seven Muslim majority nations.

It has the backing of several high profile politicians, including Green Party co-leader Caroline Lucas, former Labour leader Ed Miliband, former Liberal Democrat leader Tim Farron and London Labour MPs Tulip Siddiq and David Lammy.

Several high-profile names from the entertainment world also back the group, including singers Paloma Faith and Lily Allen, comedian Frankie Boyle and writer Caitlin Moran.

The bosses of leading unions including the TUC, the NUS, Unison, the GMB and the RMT have also endorsed the campaign.

Politicians on all sides, including Theresa May, lined up to condemn the President’s retweets, with the Prime Minister saying he was “wrong” to share the unverified videos from a “hateful” group such as Britain First, which “peddles lies and stokes tensions”, to his 45.6 million Twitter followers.

But the defiant President hit back, advising Ms May to concentrate on the problem of Islamist extremism in the UK.

“Don’t focus on me, focus on the destructive radical Islamic terrorism that is taking place within the United Kingdom. We are doing just fine," he tweeted.

Ms May, currently on a visit to the Middle East, responded by saying the UK takes the threat of terrorism very seriously, as the war of words threatened to sour the “special relationship” the two nations have long shared.

Left-wing commentator Owen Jones, a supporter of the Stop Trump group, said the planned protests were entirely justified.

Speaking on Sky News, he said: “What we are talking about here is a person who has intervened in our internal affairs to promote and support propaganda by the British neo-Nazi movement… there is a broader point here about bigotry and racism … and about Donald Trump and the nature of racism and fascism.

“If we are going to be serious about racism and Islamophobia and all the rest, that means standing against Donald Trump and all that he promotes.”

Other commentators have suggested the response to Mr Trump’s retweets are over-the-top – pointing out the US is traditionally the UK’s closest ally and that building new trading relationships is ever more important as Brexit beckons.

Home Secretary Amber Rudd urged people to remember "the bigger picture" of the UK's long history of co-operation with the UK as calls grew for him to be denied a visit to the UK.

Pointing to the “unparalleled sharing of intelligence” between the two countries, Ms Rudd said this had undoubtedly saved many British lives.

Nearly two million people have signed an online petition calling for Mr Trump’s proposed visit to be downgraded.

Downing Street has never officially commented on the proposed “working visit”, which would most likely be a scaled-down version of a full state visit – meaning Mr Trump would not meet with the Queen. The Foreign Office said that while an invitation to Mr Trump has been made and accepted, no dates have ever been set for a visit.

Britain’s ambassador to Washington, Sir Kim Darroch, revealed that Britain had formally protested to the White House.

He tweeted: “British people overwhelmingly reject the prejudiced rhetoric of the far right, which seek to divide communities and erode decency, tolerance and respect.

“British Muslims are peaceful and law abiding citizens. And I raised these concerns with the White House yesterday.”

As the row rumbled on, anti-Trump protesters are expected to demonstrate outside the the UK embassy in London this evening to make their feelings about the possibility of a visit by the President known.

Weyman Bennett, one of the organisers of the Stand up to Racism group, which is co-ordinating the embassy protest in west London, said: “When Islamophobia and racism is normalised, racist and Islamophobic attacks increase. We’ve already seen a shocking rise in hate crime – Trump’s tweets and potential visit can only make things worse.