Theresa May is coming under pressure from British Labour and Liberal Democrat politicians to call a snap general election - even before she is installed, as expected, as UK prime minister.

Within minutes of Mrs May's only rival, Andrea Leadsom, withdrawing from the race to be Conservative party leader - and so prime minister - Labour's Election Co-ordinator, Jon Trickett said: "It now looks likely that we are about to have the coronation of a new Conservative prime minister.

"It is crucial, given the instability caused by the Brexit vote, that the country has a democratically elected prime minister. I am now putting the whole of the party on a general election footing. 

"It is time for the Labour Party to unite and ensure the millions of people in the country left behind by the Tories' failed economic policies, have the opportunity to elect a Labour government".

Mr Trickett made his comments just as Angela Eagle was launching her challenge to Jeremy Corbyn's leadership of the Labour party.

Liberal Democrat leader Tim Farron also joined calls for a snap election.

"There must be an election," he said. "The Conservatives must not be allowed to ignore the electorate, their mandate is shattered and lies in ruins.

"Britain deserves better than this Tory stitch up. May has not set out an agenda, and has no right to govern. She has not won an election and the public must have their say.

"From her time as Home Secretary we know she is divisive, illiberal and calculating."

Previously Ms May said there would not be an election if she was made PM as the Conservatives have a mandate to stay in power until 2020.

But she did demand that Gordon Brown go the country when he succeeded Tony Blair as Prime Minister in 2007.

"Gordon Brown doesn't have the mandate, he wasn't elected as prime minister, and he should go to the country," she said at the time.

Last year, the Conservatives won a 12-seat majority in the UK parliament, with Labour being all but wiped out in Scotland, and the Liberal Democrats suffering big losses.

An early election can take place if a two-thirds majority of MPs agree, or if the government loses a motion of no confidence and is not replaced quickly.

It is no longer the case that a prime minister can call an early general election with the agreement of the Queen.

Downing Street sources said discussions were under way about the timing of David Cameron's departure from Number 10.