Meanwhile in the Commons, Deputy Prime Minister David Lammy has been giving an update on last week's G7 summit - a statement which, in ordinary times, would have been delivered by Keir Starmer.

Tory leader Kemi Badenoch questions why Lammy has been sent to update MPs on a meeting he did not attend.

Where is the prime minister, she asks - adding that Starmer "says he needs to stay in post for three months but then doesn't come of Parliament to do his job".

Badenoch also criticises Andy Burnham for not attending the debate.

Sarah Smith
North America editor

Image source, Reuters

It’s hard to imagine two men more different in their politics and personalities than Donald Trump and Keir Starmer.

But for over a year, Starmer became known as the “Trump whisperer”. By deploying flattery and avoiding public disagreements he was able to secure an early trade deal for the UK.

In his post last night predicting Starmer’s resignation hours before it was announced, Trump blamed Starmer's “failure” on his immigration and energy policies - two issues on which they totally disagree.

Trump told me in April that if Starmer opened the North Sea to oil and gas extraction and strengthened his immigration policies, then he "can recover” - but added: "If he doesn’t, I don't think he has a chance."

Trump will be carefully watching what Starmer’s successor does with the Defence Investment Plan. That could be crucial for what kind of relationship the next prime minister has with Trump.

The irretrievable breakdown in the Trump-Starmer relationship came over the war in Iran. Starmer's initial refusal to allow US forces to use UK air bases was considered unforgivable in the White House.

Trump will always maintain a special affection for the UK, based partly on his mother’s Scottish roots and his fascination with the Royal Family.

But his dealings with the British government and the next prime minister will be based only partly on their personal dynamic - and mostly on whether he is getting he wants.

Liberal Democrat leader Ed Davey says "changing the person at the top" will not fix the UK's "broken political system", and the electorate are "pretty fed up with the merry-go-round of prime ministers".

Davey says rebuilding relations with Europe, growing the economy and reforming social care need to be the priorities for the next prime minister - and on the man most likely to get that job, he says "let's reserve our judgement on Mr Burnham".

Image source, PA M

Hamza, 16, from Preston says: "Keir Starmer's policies were decent and I, as a student, have benefited from them, but I believe he has a weak charisma and fails to appeal to the public.

"I believe a man like Andy Burnham has the charisma and reputation to deliver to the public."

Flynn, 18, from Swindon says there "needs to be" a general election following Starmer's resignation, and adds "[Burnham] was elected by only around 77,000 people within the Makerfield constituency... he will have no country-wide mandate to govern".

Entian, 21, from Bath says he will be "sorry to see Starmer go" but says the "constant U-turning has been infuriating".

"I respect Starmer’s integrity but I do think without a change Labour would drown in the next election," Entian adds.

Hadrian, 29, from Leicester says Burnham "has to call an election" after "Labour spent years calling for the Tories" to do the same.

Image source, UK Parliament/PA

The atmosphere in the Commons was anything but stuffy as Andy Burnham was noisily sworn in a short while ago.

The new MP for Makerfield was gently mocked by opposition MPs as he entered the Commons, including shouts of "Rome is saved", "he's not the Messiah" and "water into wine".

He seemed to take it well, at one point referencing Monty Python's Life of Brian by quipping "I'm just a naughty boy" back at an MP.

Burnham was then pulled in for a lengthy handshake by Speaker Sir Lindsay Hoyle.

Henry Zeffman
Chief political correspondent, at Westminster

Image source, Getty Images

If there is any doubt that this leadership election is over before it has begun, the whoops and cheers with which around 200 Labour MPs greeted Andy Burnham as he arrived for a photo with them just now ought to expunge it.

Burnham got out his phone and took a selfie with the crowd, straining to fit them all into one screen.

Within weeks it may fall to him to fit them all into a cohesive government and political project.

Image source, Getty Images

Henry Zeffman
Chief political correspondent, at Westminster

I’m in Westminster Hall, where MPs are assembling to have their photo taken with Andy Burnham.

This is standard practice with any by-election winner - but this feels anything but standard.

The mood is beyond celebratory.

It’s impossible to separate the fact of this photo from what so many Labour MPs now see as Burnham’s inevitable move into No 10.

And it is notable to see so many senior figures from Keir Starmer’s government among those who got here earliest for a prime spot.

Among Starmer’s close cabinet allies who are in prominent positions for this photo are Rachel Reeves and Jonathan Reynolds, the chief whip — both front and centre — as well as Steve Reed and Nick Thomas-Symonds.

Image source, Getty Images

Image source, PA Media

We've also been hearing from Wes Streeting, the former health secretary who confirmed earlier today he would shelve his leadership bid and back Andy Burnham.

He praises Burnham's ability to win in Makerfield, which had "overwhelmingly rejected Labour" in the local elections in May.

Streeting says that result shows that "if Labour changes, we can still win", adding: "I think Andy is the person to lead us to do that."

He says Burnham "has got [his] full backing" and is capable of delivering the mandate Labour was elected on.

Asked if he had been promised a role in a future Burnham government in return for his support, Streeting says: "He has not offered me any jobs. That's not what our conversations have been about. This has been about ideas."

Image source, House of Commons

Andy Burnham is met by huge cheers from the Labour benches as he steps into a crowded House of Commons.

He takes the oath, following new SNP MP Lara Bird and the new Conservative MP Douglas Lumsden.

He bows his head several times as he makes his way through the chamber, and grins as he is greeted by supportive MPs.

Burnham then has a friendly exchange with the Speaker of the House of Commons Lindsay Hoyle as he formally becomes the Makerfield MP.

Image source, House of Commons

Image source, Reuters

Andy Burnham has just arrived in Westminster, where he will be formally sworn in as an MP.

You will be able to watch that moment in the Commons at the top of this page soon - and in the meantime, we'll continue to bring you the latest reaction and analysis to today's dramatic developments.

We're expecting a swearing in ceremony for new MPs to take place at around 14:30 BST in the House of Commons, which you will be able to watch at the top of the page.

Andy Burnham, the new MP for Makerfield, will be among the three MPs sworn in today, alongside Douglas Lumsden, who won a by-election in Aberdeen South, and Lara Bird - who held Arbroath and Broughty Ferry for the SNP.

New members of the House of Commons and the House of Lords take an oath of allegiance to the Crown before taking their seats in Parliament.

MPs either swear in using a religious text or take a non-religious, solemn affirmation.

Image source, PA Media

Reform UK leader Nigel Farage has repeated his call for an early general election, comparing Westminster to "Italian-style farce politics".

He says "whoever becomes the prime minister will not have been voted for by the British public", and adds that Andy Burnham did not stand at the last general election on Labour's manifesto.

Farage adds: "I really do think that my call for there to be a general election as soon as is possible - I think you'll find a lot of support for that."

Katie Thompson and Navtej Johal
Reporting from West Bromwich town centre

Sandwell Council flipped from Labour to Reform in last month's local elections, ending the party’s 47-year spell in control.

This is the kind of place the new prime minister will need to win at the next election in order for Labour to stay in power.

The response to Keir Starmer's resignation has been largely positive in West Bromwich town centre, with the majority of people saying it’s overdue.

Dave Holmes says it was right for Starmer to go, adding it was his U-turn on the winter fuel allowance that did it for him.

“About time. He’s useless. He says one thing then changes his mind,” he says, adding: “He’s bad, I don’t like him. I've not seen much integrity from him. But it’s not good to keep changing the prime minister. Let them have their five years."

Mandy Wood, 71, says it's “brilliant” news, and adds: “But nothing is going to change. I don’t like Labour, I don’t like Keir Starmer. His policies, he’s just turn around, turn around all the while.”

Sara Guest says: “We need a total change of government. He’s a weak leader but I don’t think Andy Bunham is going to be any better to be fair. In some ways we think he’s going to be worse, as he’s even more to the left than Keir Starmer is.”

Image source, ITN Pool

We've now heard more from Conservative leader Kemi Badenoch on today's developments. She says: "There are critical decisions that need to be made and the prime minister is setting out his farewell tour while Andy Burnham wants a summer holiday.

"It is really, really important that we ensure the country is being governed."

She adds that "whatever happens now we need to make sure that national security is the number one agenda", but that the next Labour leader will "still have the same problem - those Labour backbenchers who are not interested in defence and refuse to bring down the welfare bill".

David Deans
BBC Wales political reporter

Image source, PA Media / Welsh government

Wales' first minister, Rhun ap Iorwerth, has wished Sir Keir Starmer well after his resignation, but has called for a "new relationship" with his successor.

Ap Iorwerth said he was "disappointed that the Welsh government's ability to engage with the UK prime minister on issues which matter to the people of Wales" was "being hampered by the turmoil in Westminster".

Starmer had promised to meet the first minister and leaders of Scotland and Northern Ireland's governments in June, but the meeting failed to materialise.

Ap Iorwerth says: "I would like to see his successor recognising that Wales needs a new relationship with Westminster, with a focus on greater powers, fair funding, and respect for the democratic mandate delivered by the people of Wales.

"My government and I will always seek a constructive relationship with whoever is in No 10, but we have clear expectations that the respect agenda must work both ways."

Meanwhile, the interim leader of Welsh Labour Ken Skates praised Sir Keir, saying he "brought our party back from oblivion and delivered one of the greatest victories the Labour Party has seen".

More now from Andy Burnham's comments to reporters as he arrived at Euston.

First, Burnham reiterates his statement from earlier this morning - praising Keir Starmer's time in office and confirming he will stand to replace him as Labour leader and prime minister.

As we mentioned in our previous post, Burnham is then asked about a 2022 tweet, in which he called for a general election on the day Liz Truss resigned as prime minister (see screenshot above).

"I think you're jumping several hurdles ahead there - my priority today is to be sworn is as the MP for Makerfield," he says.

He says it has been "very sad" to leave Greater Manchester, where he was the mayor - saying he hopes he has left the region in a "better place".

Burnham is due to be sworn in as the new MP for Makerfield in the House of Commons this afternoon.

Andy Burnham tells the BBC that it is "jumping several hurdles" when asked if there should be a general election if he becomes prime minister.

We'll bring you more in a moment.

Andy Burnham's train has just arrived at London Euston station - our reporters on the ground will try to speak to the man on course to be the next prime minister.

He'll be formally sworn in as the new MP for Makerfield shortly.

Jamie Moughton
Reporting from the 10:54 Manchester to London train

I've just spoken to the deputy leader of the Labour Party and longstanding Burnham ally Lucy Powell on the train taking the new Makerfield MP to Westminster.

Powell praises Starmer for "turning the party around" and says the PM gave a "dignified and graceful" resignation speech.

She says the party now needs to show it can "do an orderly transition well", and says that she will make sure the process is "fair and smooth and hopefully relatively quick".

Asked if she expects a job in any future Burnham-led government, she replies: "Let's not get ahead of ourselves."

Mark Lowen
Reporting from Euston

A few dozen journalists have gathered at London Euston station, waiting for the most famous passenger of the 10:54 from Manchester Piccadilly to arrive.

Station staff are here too, knowing there’s no way to keep the cameras and microphones in check.

The scramble to get a word with the likely next occupant of No 10 is likely to be big and messy.