The Prime Minister is considering a bid to sabotage a 'coronation' of Andy Burnham by secretly lending support to Wes Streeting and triggering a full-blown Labour leadership contest, The Mail on Sunday understands.

Insiders say the Prime Minister may force Mr Burnham to go through a potentially two-month long party election process by privately allowing some of his loyal ministers to nominate Mr Streeting.

That would allow the former Health Secretary to get over the 81-MP nominations required to launch a full-scale contest in which Labour grassroots members would get the final say.

The surprise tactic comes with Sir Keir under mounting pressure from ex-mayor Mr Burnham to stand aside and allow him to become PM unopposed.

And there are also reports that former Health Secretary Mr Streeting himself will smooth Mr Burnham's path to Number 10 by not standing himself in return for becoming Chancellor in the former mayor's new Cabinet – a post coveted by Burnham ally Ed Miliband.

There are even suggestions that Mr Streeting has made it a condition of a deal with Mr Burnham that Mr Miliband, currently Energy Security Secretary, does not get the Treasury job.

Last night, party sources said that playing to 'Wes's vanity' was the key to getting him to mount a challenge.

Under Labour's internal rules, Sir Keir as party leader would automatically get on to the ballot paper without having to seek nominations himself.

One Starmer loyalist with knowledge of the ploy said: 'It's a terrible plan but it's all we have left.'

They also raised hopes that a full-scale leadership contest would flush out 'a lot of senior people who privately hate Andy'.

If they succeed, allies of Sir Keir believe the plot would force MPs to 'pick a side' – and expose what they see as so-called 'King in the North' Mr Burnham's balancing act between the Left and Right of the party.

Labour figures on the party's Right were shocked to see John McDonnell, one-time right hand man to Jeremy Corbyn, weeping with joy at the prospect of Mr Burnham in Number 10.

But Mr Burnham is also seen as someone with past credentials on Labour's Right, having been a minister under both the Blair and Brown governments.

Sir Keir's inner circle is understood to believe that an open contest would be the best way of highlighting Mr Burnham's alleged 'flip-flop' reputation and force him to pick a side. 

However, Mr Burnham's team is known to be keen to avoid a formal contest, especially if he was faced by a candidate more Left-wing than him such as former Deputy PM Angela Rayner.

Some Left-wing Labour MPs still harbour hopes that Ms Rayner, who was once tipped to be leader and topped Labour members polls, would be a candidate.

But critics say that in the last weeks and especially since last week's by-election result that Ms Rayner had 'vanished' and lost standing given the scale of Mr Burnham's victory.

One Labour veteran said: 'Angie has much less power now Andy's won so comprehensively.

'She'll still get a job but she won't be able to dictate the terms now.

'It'll be something like the so-called Ministry of Fun - the Department of Culture, Media and Sport – that she'll likely get now.'

That post is currently occupied by Wigan MP Lisa Nandy who, as a staunch backer of Mr Burnham, is now tipped for promotion.

Last night, allies of Mr Streeting said that they were not aware of any such tactics by Sir Keir and they denied they had done any job deal with Mr Burnham.

They insisted that Mr Streeting already had the support to stand and intended 'to be a candidate in a contest'.

One ally said: 'The focus this weekend is giving the PM the space to reflect on his position, to come to the right conclusion, and do the right thing.'

Downing Street denied the PM had drawn up plans to help Mr Streeting with nominations.