Morgan McSweeney warned Keir Starmer to block Andy Burnham’s return to Parliament or face ‘the end’, it was claimed last night.

The Prime Minister’s former chief of staff is understood to be once again offering advice to Sir Keir, despite exiting Downing Street in February over his role in appointing Peter Mandelson as US ambassador.

And a Labour source told the Daily Mail that Mr McSweeney was pushing the Prime Minister to prevent the Greater Manchester mayor returning to Westminster, by asking the party’s ruling National Executive Committee (NEC) to block him for a second time.

Last night, the NEC voted by a majority to allow the former health secretary to stand in the Makerfield by-election next month. 

Ahead of the decision, the source revealed: ‘Morgan is telling Keir to stop Andy via the NEC.

‘The argument is the same as before – if he lets him back in then it’s the end because Andy will challenge him immediately and he will win. 

And then you risk having a Government pursuing Left-wing ideas that nobody voted for and that could bankrupt the country.

‘Keir is currently disregarding the advice because of the backlash it would cause. But Morgan is pushing him on it.’

Morgan McSweeney (left) was reportedly pushing the Prime Minister (right) to prevent Greater Manchester mayor Andy Burnham returning to Westminster 

Andy Burnham (pictured) has been cleared to run in the upcoming by-election in Makerfield after an unprecedentedly swift and covert consultation of Labour’s ruling NEC committee

Downing Street flatly denied the claim last night, saying it was ‘not right’.

But a second Labour source claimed Mr McSweeney had even offered to lobby members of the NEC against allowing Mr Burnham’s return.

Mr Burnham was blocked in January when he tried to stand in the Gorton and Denton constituency.

At the time, Sir Keir took Mr McSweeney’s advice, despite a string of senior Labour figures warning it would be divisive to bar Mr Burnham. 

But the PM’s authority has been severely weakened by Labour’s disastrous performance in this month’s local elections.