Theresa May is facing calls to scrap Donald Trump’s visit to Britain after the US President’s latest attack on London Mayor Sadiq Khan.

Mr Trump reignited his feud with Mr Khan, just hours after wrongly claiming the mayor had said there was “no reason to be alarmed” about the risk of terror attacks in London.

Claiming he had backtracked, he tweeted: “Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his “no reason to be alarmed” statement. MSM [mainstream media] is working hard to sell it!”

Mr Khan himself refused to get involved in the row. A spokeswoman said: “The Mayor is focused on dealing with Saturday’s horrific and cowardly attack.”

But Tim Farron, the Liberal Democrat leader condemned Theresa May’s “supine relationship” with the President, saying: “Trump is an embarrassment to America.

“In the wake of three recent terrorist attacks, two of which killed people on the streets of London, Donald Trump decides to use his time in the Oval Office to attack the Mayor of London over Twitter.

"Sadiq Khan has shown dignity and leadership. Theresa May absolutely must withdraw the state visit. This is a man insulting our national values at a time of introspection and mourning.”

And David Lammy, the senior Labour MP, tweeted: “You are truly beneath contempt. You are just a troll. Show some bottle please PM. Cancel the state visit and tell Trump where to get off.”

Earlier, the Prime Minister – three times – refused to directly criticise Mr Trump’s comments about the Mayor of London, when questioned by journalists on the campaign trail.

Ms May ducked those questions twice, before eventually saying: “I think Sadiq Khan is doing a good job and it’s wrong to say anything else.”

Mr Trump is believed to have had Mr Khan in his sights ever since the mayor, last year, condemned his “ignorant” proposal to ban Muslims from entering the US, warning it would “make both our countries less safe”.

On Saturday, within hours of the London Bridge murders, the President tweeted: “At least 7 dead and 48 wounded in terror attack and Mayor of London says there is "no reason to be alarmed!”

In fact, Mr Khan had said: “My message to Londoners and visitors to our great city is to be calm and vigilant today.

“You will see an increased police presence today, including armed officers and uniformed officers. There is no reason to be alarmed by this.”

Jeremy Corbyn, the Labour leader, has hinted he could delay Mr Trump’s contentious state visit to Britain later this year if he is elected Prime Minister this week.

In an interview with The Independent last week, Mr Corbyn said he was “very concerned” about the speed in which Mr Trump received the honour by Ms May – just seven days after he took office.