LONDON - Liz Truss has confirmed she is resigning as prime minister after 45 days in office, becoming the shortest serving PM in UK history.

Truss has faced calls to quit over the disastrous fallout from her mini-budget, with pressure ramping up ever since following a series of screeching U-turns that saw party unity disintegrate.

In a brief statement outside Downing Street, Truss said: "I recognise… given the situation I cannot deliver the mandate on which I was elected by the Conservative Party.”

She confirmed she had spoken to the King in order to inform him that she was stepping down.

Her successor will be chosen within a week, though no details as to the process have yet been given.

Truss has clocked up 44 full days in the role – a long way behind the next shortest premiership, that of Tory statesman George Canning, who spent 118 full days as PM in 1827 before dying in office from ill health.

Labour leader Sir Keir Starmer called for an immediate general election in the wake of her resignation.

He said: “The British public deserve a proper say on the country’s future. They must have the chance to compare the Tories’ chaos with Labour’s plans to sort out their mess, grow the economy for working people and rebuild the country for a fairer, greener future. We must have a chance at a fresh start. We need a general election – now.”

Meanwhile, Liberal Democrat leader Sir Ed Davey has also called for a general election, tweeting: “We don’t need another Conservative prime minister lurching from crisis to crisis."

“We need a general election now and the Conservatives out of power.”

On Wednesday, Truss insisted she was a “fighter, not a quitter”, but the pressure from her own mutinous MPs proved to be too much.

On Thursday, Sir Graham Brady, the powerful chairman of the 1922 Committee of backbenchers was seen arriving at No 10 in what appeared to be a hastily-arranged meeting.

Deputy prime minister Thérèse Coffey and party chairman Jake Berry were also seen entering the building.

Things unravelled in dramatic fashion on Wednesday night after Suella Braverman resigned as home secretary over a breach of ministerial rules relating to sending an official document from her personal email.

However the real reason for her departure is understood to be a blazing row with Truss over immigration policy.

Braverman raised “serious concerns” about the government in her resignation letter, raising questions over Truss's competence and “commitment to honouring manifesto commitments, such as reducing overall migration numbers”.

There were also ugly scenes in the Commons on the same evening as Tory MPs were ordered to vote against a Labour motion on fracking.

The chaotic night prompted more Tory MPs to publicly call for the prime minister to resign.

Truss was protected from a confidence vote during the first 12 months of her leadership, but it quickly became clear she could not command the support of her MPs and it became impossible for her to continue.