Andy Burnham's march to power continued today, as he confirmed the hiring of a top former Blairite minister as his new Chief of Staff.

Mr Burnham has picked ex-cabinet minister James Purnell to head up his No. 10 operation if he becomes Prime Minister on July 17, as looks increasingly likely.

The chaotic nature of the Makerfield MP's plans for government was underlined on Tuesday night, when the news of Mr Purnell's new job leaked in the press before he had informed his own staff at lobbying firm Flint Global.

The Downing Street chief of staff is the PM's most senior political adviser, overseeing and managing the entire operation's political staff, government policy, party politics and communications.

Mr Burnham and Mr Purnell's relationship goes back 25 years, to when they were both elected to the Commons in 2001, before climbing the greasy pole together and joining the Cabinet under Gordon Brown.

After quitting government in a botched 2009 coup against Mr Brown, Purnell - an arch Blairite - joined the BBC as director of strategy before becoming CEO of Flint.

While he will bring experience to the crucial job, eyebrows were raised in Westminster over Mr Purnell's past relationship with Peter Mandelson.

Mr Mandelson, whose appointment as Washington Ambassador was a significant factor in the eventual resignation of Keir Starmer, described Mr Purnell as 'one of my boys', and 'a great friend of mine and a man of huge intellect and talent' in 2010.

That same year, Mr Purnell branded Mandelson 'a friend of mine as well as a political colleague'.

Flint Global, his lobbying firm, also took on a significant number of staff from Mr Mandelson's former lobbying outfit when it went into administration following the Epstein row.

The Mail understands that Mr Mandelson is delighted by Mr Burnham's decision to appoint Mr Purnell, according to a source close to the former ambassador.

This afternoon Mr Burnham's official spokesman was forced to insist they had done due diligence into their new star hire, and ruled out Mr Purnell having any recent friendship with Lord Mandelson.

But Labour opponents of Mr Burnham were scathing, with one senior MP ominously warning 'We cannot have that issue AGAIN', while a government source said: 'I'm starting to wonder if anyone bothered to do a quick Google.'

Pro-Starmer sources pointed to other aspects of Mr Purnell's record in public life, ranging from the MPs' expenses scandal to his support for the Iraq war.

Mr Purnell, then work and pensions secretary, avoided paying capital gains tax on the sale of his London flat in 2004, and billed taxpayers £395 for the accountant's advice on how to limit what he owed.

At the time Mr Purnell's spokesman insisted he had done nothing wrong, and said 'any allegation that James avoided capital gains tax is completely untrue'.

'To be clear that he was paying the right tax, James sought advice at the time and has since contacted the HMRC to ask them to double check. HMRC have confirmed that there is no CGT to pay.'

Concerns have also been raised about whether Mr Purnell's now-former clients may prove to be a conflict of interest in the job, with a left-wing Labour MP suggesting appointment is a 'very bad sign that [Andy] is not thinking things through enough'.

The hire was leapt on by hard-left Green Party leader Zack Polanski, who accused Mr Burnham of 'starting to feel like a bit of a Blair tribute act', adding: 'It seems it's out with the old and in with the old.'

Labour MPs remain in the dark about the ideological direction of Mr Burnham's government, largely awaiting news on who he plans to appoint as Chancellor of the Exchequer.

Speaking on Channel 4 News shortly before being appointed Chief of Staff, Mr Purnell described the incoming Prime Minister as a 'Blunketite' - a reference to Mr Blair's hardline Home Secretary.

'He was very close to David Blunkett, who obviously was in that mainstream New Labour tradition, but had been a council leader in Sheffield, was probably a bit more statist.'

A spokesman for Mr Burnham said: 'James has left Flint. He will have no ongoing financial interest in the company of any kind.'

Flint Global said: 'James has resigned from Flint. He has recused himself from all client activity and has no ongoing financial interest in the company of any kind.

'James's decision to join Burnham's team is entirely his own, and one we fully respect.'