Keir Starmer insisted he is 'very pleased' that Andy Burnham is back in the Commons today as he faced an humiliating PMQs.

The premier tried to put a brave face on his situation after finally announcing his departure in an emotional speech on Monday.

Mr Burnham is now expected to take over within weeks, with Labour flocking to show their support.

Having dodged making a statement to the Commons on the G7 summit, Sir Keir was grilled on his demise for the first time. 

Kemi Badenoch mocked the premier for being surrounded by 'traitors and deserters'. 

When Sir Keir - flanked by a grim-faced Rachel Reeves - tried to talk up his achievements, the Tory leader shot back: 'If it's all so fantastic why is he resigning?'

Turning her fire on the Chancellor, Mrs Badenoch said: 'She didn't even bother to come out into Downing Street to watch the PM deliver his resignation speech. 

'Then she turned up to get a selfie with Andy Burnham.'

The Conservative leader also took aim at Ed Miliband - now tipped by many to become Mr Burnham's Chancellor. 

'He was a failed Labour leader, rejected by the electorate, brought back from the wilderness... and when the going got tough, he jumped into bed with the Mayor of Manchester,' she said.

In a brutal snipe at Mr Miliband running for the leadership against his own brother in 2010, Mrs Badenoch added: 'It's not the first time he's betrayed someone close to him, is it?' 

Mr Burnham was not in the chamber for the exchanges.

In other developments today:

• Mrs Badenoch was confronted by Bridget Phillipson and Liz Kendall after her barbs in the Commons chamber; 
• Downing Street has said Sir Keir plans to stay as an MP for the rest of the Parliament - despite speculation he will quit the Commons immediately; 
• Blairite former Cabinet minister James Purnell is being lined up for the crucial job as Mr Burnham's chief of staff;
• Mr Burnham is said to be planning to move part of the No10 operation to Manchester, although it is unclear how the arrangements would work in practice; 
• Advisers to Mr Burnham previously called for the state pension triple lock to be scrapped. 

Opening hostilities in the House, Mrs Badenoch swiped: 'I'm much happier with my new MP than he is with his.'

Sir Keir replied: 'I'm very pleased with our new member of Parliament...'

Mrs Badenoch launched a brutal volley at Education Secretary Bridget Phillipson, calling her a 'spiteful class warrior'. 

'She taxed private schools to pay for more teachers, but the number of teachers has gone down,' she said.

'It turns out appointing a spiteful class warrior as Education Secretary was a disaster.'

Speaker Sir Lindsay Hoyle intervened to say: 'Please, can I just say, think about the language using, because when we leave this chamber, don't be surprised when constituents feel they can use the same language against each other.

'Let us show a little bit more decorum and respect to each other.'

A spokesman for Mrs Badenoch said afterwards that she had been nice to Sir Keir in and felt sorry for him.

'There was very little aimed at the Prime Minister,' the spokesman said.

'This was about a Cabinet which has let him down, about a group of Labour MPs who have let him down and now they've got rid of him.'

Labour MPs including Ms Phillipson and Science Secretary Liz Kendall are understood to have confronted Mrs Badenoch after the exchanges, but she insisted they were 'destroying children's lives'. 

Despite the commitment from No10, there is scepticism that Sir Keir will stay in the Commons for the next three years.  

David Cameron, Boris Johnson and Tony Blair all stood down soon after losing power, although Rishi Sunak, Theresa May and Gordon Brown all opted to stay on. 

As a former Director of Public Prosecutions, he could return to the bar. However, human rights lawyers at his previous base, Doughty Street Chambers, are said to have been infuriated by a speech warning that Britain risks becoming an 'island of strangers' - even though he subsequently tried to walk the comment back. 

The Government push to curb jury trials has also gone down badly with former colleagues. 

'There is absolutely zero chance of Keir Starmer being welcomed back, even if he wanted to return. There is a lot of bitterness over the juries policy and the strangers comments,' one source told The Times. 

One lawyer close to Sir Keir suggested that he could be 'recruited for some major international role, possibly even UN secretary-general'. 

The current holder of the job, António Guterres - a former PM of Portugal - is due to retire by the end of this year. He is currently in the UK for a climate conference.

One source told the paper Sir Keir was 'incredibly well regarded globally as a safe pair of hands, who is thoughtful and hardworking'. 

'An international role won't require the showmanship of domestic politics. And everyone on the global stage thinks he's an amazing politician,' they added.

One Government source pointed out that no leader of a state that is a permanent security council had ever become UN Secretary General.

No10 has refused to be drawn on whether the premier will trigger a by-election. 

But a Labour veteran joked that Sir Keir would be the perfect candidate for the UN. 'Completely ineffectual? Tick.' 

Sir Keir is fighting to keep some semblance of control over the Government, although he is now blocked from announcing any radical new policies.

The PM is desperate to finalise the long-awaited Defence Investment Plan before he heads to a Nato summit on July 7 - where he will meet Donald Trump.

However, Mr Burnham's team are adamant that the decisions on defence spending should wait until he takes charge, likely on July 17. 

It has emerged Mr Burnham is drafting in a Blairite former Cabinet minister to be his chief of staff as he gears up for No10. 

James Purnell quit Gordon Brown's Government in 2009, later becoming a senior executive at the BBC.

He and Mr Burnham were contemporaries in the New Labour era, sharing a flat and playing together in the 'Demon Eyes' football team.

The appointment raises fresh mystery about the direction of Mr Burnham's 'Manchesterism' project.

Mr Purnell has always been seen as on the moderate wing of the party, having resigned party because Mr Brown was not willing to cut welfare. 

Ed Miliband's allies played down the idea it is a setback for his hopes of becoming Chancellor.

One Labour aide voiced concern about what 'due diligence' had been conducted, as he was a protege of Peter Mandelson.

Another pointed out that Mr Purnell had not been in politics for more than a decade and could find difficult to 'get back into rhythm'.