Britain's next prime minister could be known by Monday

Liz Truss walks back into 10 Downing Street after making a statement where she announced her resignation as British prime minister on Thursday.

The race to replace Liz Truss and become Britain's third prime minister since the start of the summer could be decided by Monday — with Boris Johnson among the expected runners.

Ms Truss's resignation came after just 45 days in office during which a mini-budget crashed the markets, she lost two key ministers, and lost the confidence of almost all her own MPs.

Mr Johnson, who himself quit in disgrace in July after a series of scandals that left his personal integrity in tatters, was expected to fly back from the Caribbean where he has been on holiday with his family.

The Guardian quoted one ally as saying Mr Johnson feels it is in the “national interest” for him to stage a return, while another said the former prime minister felt his reign had been unfairly “cut off before its time” and that he still has plenty to do.

Boris Johnson makes a speech outside 10 Downing Street, before formally resigning as prime minister on September 6.

Shortly after 1.30pm yesterday, a little over 24 hours after insisting she was "a fighter, not a quitter", Liz Truss stood at a lectern in Downing Street and said she had informed the King of England that she was resigning, making her Britain’s shortest-serving prime minister ever.

She said she recognised she "cannot deliver the mandate" which party members gave her a little over six weeks ago when she replaced Mr Johnson.

What next?

There is an acceptance that her replacement needs to be found quickly, so candidates in the latest leadership race will need the support of 100 of the 357 Tory MPs to make it onto the ballot paper. 

It is hoped that will eliminate the need for a time-consuming vote among ordinary members — the contest to replace Boris Johnson lasted longer than Ms Truss's premiership.

Nominations will open on Thursday night and close lunchtime on Monday. If only one candidate secures the nominations of 100 MPs, there will be no vote for party members and that candidate automatically becomes party leader and prime minister on Monday.

'A fresh start'

Liz Truss's resignation triggered yet more calls for a general election in Britain. Labour leader Keir Starmer demanded an election "now" so that Britain can have "a chance at a fresh start".

Labour leader Keir Starmer has led the calls for a general election. Picture: Stefan Rousseau/PA Wire

Without a general election, the Conservatives will be on their third prime minister on the mandate won by Johnson in December 2019.

Taoiseach Micheál Martin told reporters in Brussels he "sympathises" with Liz Truss on a personal level, but said it is important her replacement is found as quicky as possible to ensure financial stability.

He also said there is a window of opportunity for her successor to address the issues around the Northern Ireland Protocol Bill.

Whoever becomes the new British prime minister, we would hope, given all that’s going on in Europe and the world, that a meaningful discussion would take place with the European Union to resolve the issues,” he said.

Speaking prior to her resignation, Tanáiste Leo Varadkar said the British Labour party had signalled to him that it would want a closer relationship with the EU if there was a Labour party government in the future.

Mr Varadkar met with Mr Starmer in London on Wednesday and said Mr Starmer told him that they would work very closely with Ireland and would also seek a closer trading relationship with the EU.