Wes Streeting swiped at Andy Burnham today as he warned against Labour leader hopefuls making 'expensive popular promises' that cannot be kept.

The former health secretary insisted the brewing contest to succeed Keir Starmer cannot become a 'Dutch auction' to appeal to Left-wing activists.  

In a speech in the City, Mr Streeting said 'fiscal discipline matters', in a barb at Mr Burnham's previous suggestion he could take on the bond markets.

He was also adamant that he has the 81 supportive MPs needed to enter a leadership race.

The intervention comes as Sir Keir's grip on power looks to be loosening, with Mr Burnham trying to return to the Commons this week.

The PM, in France for the G7 summit, told broadcasters this morning that he will not 'walk away' from No10 without a fight. 

But the mayor's allies are plotting an immediate bid to oust the PM if he wins the Makerfield by-election. 

That is despite signs that Mr Burnham's personal ratings have already been slumping as the public sees more of him.  

Mr Streeting again condemned the idea of a 'coronation' for the next leader in his speech this morning. 

He said: 'There is a risk that a Labour leadership contest becomes a Dutch auction of the most expensive and popular pledges to appeal to the party faithful at the expense of the British people. Not on my watch.

'We can't play fast and loose with the public finances or the trust of the people. Not when the risks are so high and faith in politics is so low.

'As I've said on my leaflets in Ilford North at every general election: you may not always agree with me, but you'll always know where I stand.

'You won't find me making pledges to win your vote in a leadership election only to let you down after the ballots are counted.'

In a shot at Mr Burnham - who previously criticised the Government for being 'in hock' to the bond markets - Mr Streeting added: 'Bond markets are not Bond villains and fiscal rules matter. Fiscal discipline matters because credibility is the precondition for an activist state. 

'With debt approaching 100 per cent of GDP, Britain has very little room for error.'

The markets have been spooked by signs that Mr Burnham could take Labour to the Left with a major spending splurge funded by borrowing and even more tax.

He has hinted at wealth taxes, revaluing council tax and called for nationalisations.

But Mr Burnham has also executed screeching U-turns on a slew of ideas, including ruling out billions of pounds of compensation for so-called WASPI women just hours after supporting the prospect. 

Asked whether he had the 81 Labour MPs needed to enter a contest, Mr Streeting replied: 'As much as I can, I am going to resist being drawn into politics, process, personalities, because I want the contest to be a battle of ideas, not just a clash of personalities or an obsession with political drama.

'Yes I have the support I need to be on the ballot. Yes, I think we will be better served if that is a contest and a battle of ideas, not just of personalities.

'And indeed I don't think we should allow petty factional interests to get in the way of what I think is a necessary and urgent debate about how progressive politics can shape this country for the better, because we know what the alternative is.'

He pointed to the results of May's elections, which resulted in nationalist parties 'in power in every corner of the United Kingdom'.