Greater Manchester Mayor Andy Burnham has been cleared to seek selection as Labour's candidate in a by-election which could pave the way for him to return to Westminster.
The mayor has been given the go-ahead by Labour's ruling National Executive Committee (NEC), which blocked his previous attempt to stand in a by-election in January.
If he is selected as the candidate in Makerfield, in the north-west of England, and goes on to win, Burnham is widely expected to try to replace Sir Keir Starmer as prime minister.
The prime minister is continuing to resist calls to stand down and set a timetable for his departure and is expected to fight any challenge from Burnham or other likely contenders.
The Makerfield constituency became vacant on Thursday, when Labour MP Josh Simons said he would resign to make way for Burnham.
The BBC understands the by-election is likely to take place on 18 June.
On Friday, the prime minister was in a police control centre in London but did not take questions from the media.
Steve Reed, the housing secretary and an ally of the PM, said: "It's been a very difficult week but we need to take a breath now, take this weekend to reflect on what's going on, and come back next week and focus on the country we were elected to serve."
Events have calmed down after a frenetic week of political activity which has seen the prime minister defy calls to step down, following his party's disastrous election results.
Nearly 90 Labour MPs have urged Sir Keir to go and five ministers have resigned but a leadership race cannot be triggered until someone, with the backing of 81 Labour MPs, formally challenges the prime minister.
Under Labour Party rules, Burnham is unable to join a leadership contest unless he becomes an MP.
Announcing his decision to apply to stand in Makerfield, Burnham said he wanted to "bring the change we have brought to Greater Manchester to the whole of the UK and make politics work properly for people".
He added that he would "not take a single vote for granted".
Applications to enter the process to become Labour's candidate close on Monday 18 May and a selection meeting will take place on 21 May.
Traditionally, Makerfield has been a safe Labour seat, but more recently has been leaning towards Reform UK and, if selected, it could prove a tricky race for Burnham to win.
Wes Streeting has been seen as a potential leadership candidate and speculation that he would launch a challenge mounted on Thursday when he resigned as health secretary.
Streeting called for a broad debate about what comes next but did not say he would run for leader.
His allies say he has the support of the 81 Labour MPs needed to enter a race.
In a post on social media, Streeting said he welcomed Burnham returning to Parliament, saying: "We need our best players on the pitch."
Former Deputy Prime Minister Angela Rayner has told the Guardian newspaper that she did not rule out running but would not "trigger" a leadership race.
Conservative leader Kemi Badenoch said: "Andy Burnham wants to rock up and just be prime minister despite being out of Parliament for a decade."
Reform UK's deputy leader Richard Tice said his party would be "throwing everything possible" to ensure a "seismic" win in the by-election.
The Green Party said: "We've learnt from our campaigning and wins in Gorton and Denton and the recent local elections, and we've shown we can beat Reform."
Home Office Minister Mike Tapp said he was sorry for the past few weeks of leadership speculation, telling an audience at BBC Radio 4's Any Questions he wanted to "take this opportunity now, from my heart, to apologise to the public and to everybody in this room and every listener for what you are seeing.
"This is not what I was elected to do."
"Seeing what's unfolded in front of us over the last few weeks has been really, really painful for me," he said, adding he wanted to "get on" with his job of "fixing a rather woeful inheritance".
Labour MP Neil Coyle told BBC Newsnight that Burnham had been trying to replace Sir Keir for a long time "and frankly some of us are sick of it".
He said the NEC should block his candidacy, urging the committee to "stand up to the ego of one man".
Speaking to the same programme, Labour MP Olivia Blake said Burnham "would be a great addition back into Parliament… he's done great things in Manchester.
"He can cut through in a way we have been failing to cut through."
