So, how soon will a contest begin?
Sir Keir said he wanted nominations to open on July 9 for the Labour leadership and be completed by the time Parliament breaks up for the summer.
This is likely to mean the parliamentary stage of the contest being completed by July 16, the last day before recess.
If Andy Burnham, whose return to Westminster hammered the final nail into Sir Keir’s political coffin, is the only candidate, he could become Labour leader by July 17 or 18.
Labour’s rules mean getting onto the ballot can be a complex process, with candidates requiring the backing of 81 MPs, 20 per cent of the party’s parliamentary strength.
What if there is a leadership election?
If there is a contest, the new leader will be in place by September 1, when MPs return to Westminster.
To compete in a contest, having secured the required support of MPs, they need to receive nominations from either five per cent of constituency Labour parties, or three affiliated organisations (which must include two trade unions) which represent five per cent of affiliated membership.
Andy Burnham is widely believed to already have the necessary support from MPs to get onto the ballot in any Labour leadership election
PA
Only after passing those two stages will candidates go before the party membership.
Labour’s ruling national executive committee (NEC) will meet shortly to agree the timetable for the contest.
Could anyone stand against Andy Burnham?
Former health secretary Wes Streeting has ruled out standing against Mr Burnham, and said he will back the Makerfield MP for the premiership.
He had previously repeatedly insisted he had the 81 names required to mount a leadership bid, and spent weeks after resigning from Government setting out his stall.
The question now remains whether anyone else will throw their hat in the ring to be Sir Keir’s successor.
Former armed forces minister Al Carns could enter a leadership race
PA
Former Royal Marines officer Al Carns, who quit as armed forces minister in a row over defence funding and the treatment of Northern Ireland veterans, has previously hinted he would seek to enter a leadership race.
Following Sir Keir’s resignation, he did not explicitly rule out standing in a contest, but signalled he might not make the leap, writing on social media that Labour needed to “to see if we can get our act together and focus on the work we were elected to do. That’s where my focus is now”.
What happens to Sir Keir Starmer now?
He remains Prime Minister until the King appoints his successor.
Sir Keir is expected to represent the UK at the Nato summit in Turkey which starts on July 7, appearing alongside other world leaders including US President Donald Trump at a time when his own authority as Prime Minister has evaporated.
The Prime Minister’s final act on the international stage could be at the UK-EU summit on July 22, with efforts to repair relations with Brussels forming a key part of his political legacy.
What will Sir Keir Starmer do next?
There has been widespread speculation he could be offered an international role, either as foreign secretary or in some other capacity.
But in his resignation speech, Sir Keir appeared to indicate he will be spending more time with his wife, Lady Victoria Starmer, and their two teenage children.
His voice choked with emotion, he said: “When I leave the biggest job in the country, I shall spend more time on the most important job: being the best husband I can to my fantastic wife, Vic, who has been a rock by my side through good times and bad, and being the best dad I can to my beautiful children, who are my pride and my joy.”
