Using the WhatsApp messaging service, he instructed his private secretary to tell staff gathered in his departmental headquarters on the afternoon of January 13 , the day before his decision, that it was “final”.

Months earlier, Jenrick watched a promotional video of the Westferry scheme on Desmond’s iPhone at a Tory fundraiser at the Savoy Hotel and agreed to a site tour.

The unsuspecting official, who was at the heart of the decision, said they were shocked by Jenrick’s urgency as they warned him of the legal risks of the scheme and a likely judicial review.

They left with the impression: “We had to get with the programme or go away.”

The source’s claim that Jenrick showed “total disregard” for the law in the run up to the decision will reignite calls for his resignation.

Those present on the fourth floor of 2 Marsham Street, a government building in Westminster, included Steve Quartermain, England’s most senior planner, planning officials and civil service lawyers. None was aware of Jenrick’s potential conflicts of interest.

Jenrick withdrew his approval in response to a legal challenge from Tower Hamlets council last month, accepting that it was “unlawful” due to “apparent bias”.

Steve Reed, the shadow housing secretary, said: “These explosive revelations show Mr Jenrick has new and very serious questions to answer.”

He added: “Labour last night called on the government halt its plans to move housebuilding powers from local councils to the housing secretary.”

The latest revelation comes amid fresh evidence of Boris Johnson’s own contact with Desmond, who also avoided paying £106m after the government waived affordable housing rules.

In an interview, the tycoon reveals that Johnson told him that he would change gambling rules to help his business after he lobbied him at a Downing Street event.

According to Desmond, Johnson “ran up to him” and said he would raise the maximum legal jackpot for his Health Lottery to £1m. He said: “He [Johnson] agreed it . . . He said, ‘Right, good news for you. We’re gonna do it.’”

Their conversation at a reception for business leaders took place on September 17, as the government considered whether to approve the Westferry plan. Desmond insisted that they did not discuss it at the event.

Last week, Sir Mark Sedwill, the cabinet secretary, said Johnson considered the Westferry case “closed”.

However, the detailed account of Jenrick’s conduct in the run-up to the decision will raise fresh questions of the minister. Jenrick has only stated that he “told” his private office of his meeting with Desmond.

Alex Thomas, a programme director at the Institute for Government, said it would have been appropriate for Jenrick to put his potential conflict in writing given that he decided not to recuse himself from the process.

He said such a document would have been a “note or an email to his principal private secretary” and that it would outline “what happened at the event, why he felt no substantial discussion had taken place, and that no further contact with the applicant would occur.”

Last night, a government spokesman said: “As made clear in the secretary of state’s letter to the [housing, communities and local government] select committee, this was a thorough decision-making process, approached with an open mind, with no question of bias. The secretary of state read the [planning] inspector’s report and representations from parties and took advice from officials throughout the process.”

The Ministry of Housing, Communities and Local Government said:“A full account has been sent to the HCLG select committee by the secretary of state and the department has published relevant documents online. We have nothing further to add.”

A spokesman for 10 Downing Street said: “The government’s position on society lottery rules has been set out by DCMS and the Gambling Commission, following open public consultation by both.”

Minister in a hurry told officials: It’s my way or the highway

Jenrick was a man in a hurry. It was less than a week after MPs had returned to parliament following their Christmas recess when the 38-year-old housing secretary dispatched his private secretary to relay orders to some of his most senior civil servants.

On the afternoon of January 13 they huddled in a breakout area on the fourth floor of 2 Marsham Street, the glass building in Westminster that is home to the Ministry of Housing, Communities and Local Government, which Jenrick heads.

Jenrick’s aide quickly got to the point. The secretary of state wanted to issue a decision letter the next day approving the Westferry scheme on the Isle of Dogs.

According to a civil servant at the meeting, his aide was texting to Jenrick on WhatsApp as the meeting unfolded. The source, who has come forward to detail the minister’s “disregard for due process and accountability”, said that officials were left in no doubt that their views were not welcome.

The aide is claimed to have said: “We’re going ahead with this. It’s the secretary of state’s decision. It’s final.”

Those gathered around a table near the fourth-floor atrium included Steve Quartermain, England’s most senior planning official, communications advisers and government lawyers.

None knew Jenrick had a potential conflict of interest that would soon imperil his career: he had sat next to Desmond at a £900-a-head fundraising dinner just eight weeks earlier at the Savoy in London, where the tycoon had shown him a promotional video of the scheme. Desmond had later implored Jenrick to act quickly, so he would avoid a £30m-£50m Tower Hamlets council community infrastructure levy that would come into force in mid-January, joking in a text: “We don’t want to give the Marxists loads of doe [sic] for nothing!”

The civil service source is insistent that key officials on the case were not informed of Jenrick’s contacts with Desmond. They also allege that Quartermain and Richard Watson, head of the national planning casework unit, practically “begged” him to think again about the decision. Both are said to have been met with indifference.

At the meeting, Quartermain, a moustachioed Durham University graduate who has since left the civil service after several decades, raised his objections one last time. “Look,” he is said to have remarked. “The visual impact of it is terrible. There are policies around tall buildings in that particular area. It’s too big. It’s too tall. It’s too dense.” One of the lawyers weighed in, too, saying the scheme did not comply with affordable housing rules and warning there was a “70% to 80%” chance of a judicial review.

Others expressed concern that Jenrick wanted to blame the delays in Westferry on the London mayor, Sadiq Khan, and Tower Hamlets, while touting his approval as a victory for the Conservative government’s housebuilding programme. His aide then delivered the coup de grâce. “Look, guys,” she said. “The secretary of state has made his mind up . . . Let’s get this letter sorted out.” The source recalled: “We all sort of went away.”

In the months building up to the decision, civil servants had argued that Jenrick should reject the Westferry scheme, saying it violated planning rules on several counts and would be dead on arrival if challenged in court.

Not only had he ignored them. He had asked them during purdah — the pre-election period when civil service activity is restricted — to prepare for a decision in the first days of a new government, owing to “sensitivity with timing”.

Why did Jenrick refuse to listen? Why was he in such a rush? And why did officials not know about his dinner with Desmond?

Last month the minister performed a U-turn and consented to his approval being quashed in court, acknowledging that his decision had been “unlawful” as a result of his own “apparent bias”.

But questions have not gone away. First, it emerged that Jenrick approved the plan 24 hours before the levy would have kicked in, saving Desmond millions. Then it transpired that Desmond had donated £12,000 to the Tory party shortly after the decision.

On Wednesday the release of heavily redacted documents shed fresh light on the circumstances of the “cash for favours” scandal.

They showed that Jenrick swiftly texted Desmond after the dinner and agreed to go on a site tour of Westferry and that he also knew about the levy. The documents provide no evidence that Jenrick declared a conflict of interest or detailed his conversations with the billionaire to departmental officials. In Jenrick’s favour, he did not go for the tour, texting Desmond: “I think it is best that we don’t meet until after the matter has been decided.”

For Johnson, this text was enough to conclude that the matter was closed and Jenrick’s seat at the cabinet table was safe. Sir Mark Sedwill, the cabinet secretary, announced that there would be no further investigation.

It is a decision that both reflects Boris Johnson’s authority, given his majority of 80, and his disdain for the vicissitudes of life in the Westminster bubble, having ridden out many scandals himself. It also shows the minister’s proximity to No 10 and his circle of friendships in the upper echelons of the Johnson government.

Jenrick, a father of three and a former director of the auction house Christie’s, was one of three young MPs to back Johnson early in the Tory leadership contest. The others were Rishi Sunak and Oliver Dowden. All were rewarded with plum cabinet posts. Jenrick also boasts of his friendship with Carrie Symonds, Johnson’s fiancée.

Some MPs bristle at his obvious ambition and refer to him as “Robert Generic”. One MP said: “There’s a suspicion that he doesn’t actually believe in anything. He just wants to move up the ladder.” They added that unlike Sajid Javid, the former chancellor, there were “few” points of principle over which he would plausibly resign.

Few doubt Jenrick’s networking skills. He is one of the best-connected ministers in the cabinet, having served as parliamentary private secretary to the then home secretary Amber Rudd and to three leading Brexiteers — Michael Gove, Liz Truss and Esther McVey.

Such friendships may have helped when he faced calls to resign after travelling 150 miles to his manor in Herefordshire at the height of lockdown in April. Jenrick, who is married to Michal Berkner, a wealthy corporate lawyer nine years his senior, claimed that the grade I listed mansion was his family home, although neighbours quickly disputed the claim — as did his own website, which said he lived in London and at his constituency of Newark, Nottinghamshire.

Others believe that Johnson may be protecting Jenrick because of his own links to Westferry. As mayor of London, he gave an earlier, less ambitious version of the Westferry plan his approval in 2016. Sir Edward Lister, now the prime minister’s chief strategic adviser and then deputy mayor for planning, was the person behind the decision, and is said to retain a keen interested in planning.

The disclosure that Johnson and Desmond met on September 17 at Downing Street will do little to quell claims that Desmond enjoys preferential access to No 10, despite his later denial that he lobbied Johnson about the development on this occasion.

Few believe that Jenrick is as “unsackable” as Dominic Cummings, Johnson’s chief aide. One minister said that talk of a reshuffle had returned over the past week, with Jenrick, Gavin Williamson, the education secretary, and Thérèse Coffey, the work and pensions secretary, the most likely to be demoted. Coffey is said to have challenged Johnson in a cabinet meeting over the rumour, telling him that civil servants went on a “go slow” every time there was speculation about her future. Another source claimed to have spotted a reshuffle whiteboard on a recent visit to No 10.

For the moment, though, the government has shown it will spend considerable political capital on protecting the housing secretary.

It was reported last week that the prime minister had excised an announcement on key planning reforms from a upcoming speech on rebuilding Britain after Covid-19, with the express aim of sparing Jenrick further scrutiny.

The move, if it goes ahead, would give Jenrick greater power to decide on planning applications by creating a new system of development corporations.

Sir Keir Starmer, the Labour leader, has not yet called for Jenrick to be sacked and would instead prefer for the scandal to go on as long as possible, leading to more scrutiny, revelations and damaging headlines. In the meantime, Steve Reed, the shadow communities secretary, has referred Jenrick to the parliamentary commissioner for standards.

One of the core issues any inquiry will address is how much Jenrick told civil servants about his contact with Desmond.

The fact that no such documents were forthcoming last week is why a senior civil servant who was at the heart of the Westferry decision has come forward today to explain Jenrick’s approach to the development and the civil service generally. The whistleblower said: “Robert Jenrick has pretty much been the worst secretary of state that I’ve had the pleasure of working for.”

They claimed Jenrick had ignored or rejected advice on other occasions and expressed little appreciation of his quasi-judicial role as housing secretary — that is, someone who must make decisions based on planning law, rather than politics.

Any hint of bias can derail a project, which is why planning decisions are usually announced in sober and legalistic letters. But Jenrick is said to have overruled officials and demanded politically charged announcements on controversial plans, including a proposed Holocaust memorial in Westminster and an Indian museum in Camden, north London.

Civil servants are said to have expressed their displeasure to Tom Kennedy, his special adviser, only to be told that Jenrick had “made his decision”. He now faces another High Court battle and judicial review over his decision on the Holocaust memorial.

The whistleblower said Jenrick further infuriated civil servants during the general election campaign, when he insisted the department spend taxpayers’ money buying Facebook ads to promote the Towns Fund, a communities initiative.

The ads apparently violated purdah rules by pledging Tory investment in “red wall” seats. In a “standoffish” meeting about the Towns Fund attended by his special advisers, Jenrick is said to have told a senior civil servant that it was, in effect, “My way or the highway . . . We had to get with the programme or piss off. It was that simple.”

The source said: “The arrogance of the man was just astounding. He wouldn’t listen to anything the civil servants were saying to him. He really had a political ambition, which he was trying to use us to support.”