Dominic Cummings asked Boris Johnson to sign a contract giving him special powers in Downing Street, The Telegraph has learned.

Although employed under the lowly title of "assistant to the Prime Minister", Mr Cummings is understood to have a special agreement, believed to carry Mr Johnson’s signature, spelling out his authority over special advisers (SpAds).

It also confirms his jurisdiction over other government projects such as ARPA, the Tories’ pledge to recreate the United States’ Advanced Research Projects Agency in Britain.

The revelation underlines the extent of the power wielded in Number 10 by the controversial former Vote Leave campaign director, who was once described as a "career psychopath" by David Cameron.

Tony Blair was criticised when he gave his press secretary, Alastair Campbell, and Jonathan Powell, his chief of staff, special powers to order civil servants to do their ministers' bidding following his election in 1997.

Yet while Mr Blair used an order in council - an administrative procedure similar to the royal prerogative - the agreement between the Prime Minister and Mr Cummings is a personal contract without the same legal standing.

A Downing Street insider said: “Before he took the job, Dom made Boris sign a contract specifying what his powers were to be, that he would be allowed to hire and fire SpAds [and] confirming his authority over other key government projects.”

Another source said the pair came to the agreement at a private meeting in Downing Street the Sunday after Mr Johnson won the Tory leadership race on July 23, when he asked Mr Cummings to be his right-hand man.

“Boris asked Dom to come in and offered him the job, and Dom said, these are the areas I want control over: SpAds and personnel, and other key policy areas including the ARPA stuff, and I think some immigration policy and perhaps even reforming the civil service.”

On Thursday, Downing Street launched a new open application process for SpAd roles to attract more recruits from the corporate and professional arena with experience of advising business leaders and other senior figures - and fewer "Westminster lifers".

According to a job ad placed on a new website Spadjobs.uk, Number 10 wants applicants with a "track record of success working in communications or digital fields to apply" to help "effectively tackle long-term problems and take advantage of the opportunities Brexit has opened up".

The recruitment drive came after Sajid Javid resigned as Chancellor over a move to replace his SpAds with a team of aides controlled by Downing Street.

Mr Javid launched a thinly veiled attack on Mr Cummings during his resignation speech to the Commons on Wednesday, when he appeared to lay the blame for his departure at the adviser’s door.

Mr Javid’s resignation during the Feb 13 reshuffle followed rumours of tensions between Mr Javid and Mr Cummings, amid claims Number 10 feared the fiscally cautious Treasury was trying to rein in Mr Johnson’s ambitious spending plans.

Mr Javid said: "It has always been the case that advisers advise, ministers decide and ministers decide on their advisers.

He added pointedly: "I don’t intend to dwell further on all the details and the personalities … the 'comings' and goings if you will."

But Mr Javid also claimed much of the commentary on his relationship with Mr Cummings was "just gossip and distraction".

Shadow Chancellor John McDonnell tweeted that Mr Javid had launched a "damning attack" on Mr Cummings' "dominance" of the Johnson administration.

Mr Cummings has recently courted criticism over his hiring of Andrew Sabisky to shake up Whitehall. Mr Sabisky, a "super forecaster" adept at predicting future trends, was forced to resign after it emerged he had previously made controversial comments about race and eugenics.

A Downing Street spokesman said Mr Cummings "has all the usual responsibility someone in his position has".