Sir Keir said the country "can not have another experiment at the top of the Tory party".

Liz Truss resigned as prime minister after just 45 days in the job, claiming she "cannot deliver the mandate on which I was elected".

A new prime minister is expected to be announced by 28 October.

It will be the second Conservative Party leadership election this year.

The Liberal Democrats, the SNP and the Green Party have also been calling for an immediate general election.

SNP Westminster Leader Ian Blackford MP said the "utter chaos at the centre of the Tory government cannot continue any longer".

Liberal Democrat leader Ed Davey said: "We do not need another Conservative prime minister lurching from crisis to crisis, we need a general election.

"It is time for Conservative MPs to do their patriotic duty, put the country first and give the people a say."

The next general election is not due to take place until at least 2024, after the Conservatives won a landslide majority in the last one in 2019.

Ms Truss was elected by the Tory membership in September, but she lost authority after a series of U-turns.

In a brief speech outside Downing Street, Ms Truss said the Conservative Party had elected her on a mandate to cut taxes and boost economic growth.

But given the situation, Ms Truss said: "I recognise that I cannot deliver the mandate on which I was elected by the Conservative Party."

Ms Truss said she would remain in post until a successor formally takes over as party leader and is appointed prime minister by King Charles III.

She will become the shortest-serving PM in British history when she stands down.

Leading pollster Professor Sir John Curtice said whoever leads the Conservative party next should "enjoy the next 18 months to two years, because that will probably their tenure".

"Parties and governments who preside over a fiscal crisis have nearly always struggled at the ballot box at the next election," Sir John said.

An Opinium poll this week projected a 1997-style landslide for Labour, with the party winning 411 seats.

The same poll, conducted for the TUC interviewing more than 10,000 adults, predicted the Conservatives would be reduced from 356 MPs to 137.

Sir Keir said: "This is not just a soap opera at the top of the Tory party - it's doing huge damage to the reputation of our country.

"We need a general election so the public can have their say on this utter chaos.

"There is an alternative and that is a stable Labour government. We are ready to form a government and stabilise the economy and implement a real plan for government living standards and help people through a cost of living crisis. "

In his speech to the TUC conference earlier, Sir Keir said the Tories were too bogged down with "pathetic squabbles" to govern the country.

Sir Keir said Labour had a long-term plan to "deliver cheaper bills and higher living standards for working people, growth and jobs in every part of our country".

He outlined some of the policies he announced at Labour's annual conference last month, including those in its "green prosperity plan"

The plan includes pledges to create a publicly owned renewable energy firm, achieve carbon-free electricity by 2030, and insulate 19 million homes.