Cabinet ministers have expressed concern about Keir’s Starmer’s decision to sack Olly Robbins as the Foreign Office’s top official over the Peter Mandelson vetting scandal as they warned him not to alienate the civil service, sources have told the Guardian.

Several ministers spoke out about the decision to sack Robbins during a gloomy cabinet meeting on Tuesday, according to multiple government sources.

Those who intervened included the deputy prime minister, David Lammy, who warned against creating a “them and us” mentality between ministers and officials, as Whitehall reels in the fallout from the vetting scandal.

The home secretary, Shabana Mahmood, is understood to have questioned whether it was justifiable to sack Robbins for his failure to tell Starmer that Mandelson had failed vetting, and then to praise him as an outstanding civil servant.

Three others, including the health secretary, Wes Streeting, and the chancellor, Rachel Reeves, warned the prime minister not to pick fights with officials and instead to keep them “on side” – a position with which Starmer said he agreed.

The discussion – which one source described as a “disagreement” – is the latest sign of deep unease within government at the Guardian’s revelation that Mandelson was appointed Washington ambassador despite having failed vetting checks.

Robbins, who was sacked within hours of the Guardian’s report, confirmed to MPs on Tuesday he had not told anybody in Downing Street about the advice of vetting officials not to grant Mandelson clearance.

One senior cabinet minister is understood to believe that the top official should not have been sacked, but should have been suspended instead until all the facts were available.

But many in the Labour party believe his testimony – during which he described heavy pressure from Downing Street to confirm Mandelson in post – raised questions about the prime minister’s judgment and risked exacerbating tensions with Whitehall.

One source said: “There was a lengthy discussion in cabinet about the fallout from Robbins’ departure. There were questions about how we were supposed to justify this to others given we were also saying what an honourable civil servant he was.”

According to a readout from Downing Street, the prime minister said Robbins “made an error of judgment, but … is a man of integrity and professionalism”. According to No 10 he also said “there are thousands of hard-working civil servants across the country who are full of integrity, doing excellent work every day with a profound sense of public duty”.

The revelation Mandelson was made ambassador to the US even after vetting officials recommended he be denied security clearance has sent shock waves through the government and once more called the prime minister’s future into question.

Starmer has said he regrets appointing Mandelson, whom he sacked after less than a year in the job after it emerged he had a closer relationship with the child sex offender Jeffrey Epstein than previously acknowledged.

The prime minister says he was not told about the original vetting advice, which was overruled by Robbins. But MPs are questioning why Starmer appointed Mandelson in the first place and why he then sacked Robbins for giving him security clearance.

That unease was underlined on Wednesday morning by the work and pensions secretary, Pat McFadden, who repeatedly declined to say whether he thought Robbins’ sacking was fair. “I think very highly of him,” he told Times Radio. “I think if the prime minister has made the judgment that he’s not got confidence in the head of the Foreign Office, then it’s difficult to continue.”

McFadden is understood not to be one of those who intervened during the cabinet debate on Tuesday.

Former senior Whitehall chiefs have called for Robbins to be reinstated. Simon McDonald, one of Robbins’ predecessors at the Foreign Office, wrote in the Guardian on Wednesday that the prime minister had “rush[ed] to a wrong judgment”.

The former cabinet secretary Mark Sedwill wrote a letter to the Times saying: “The prime minister should retract his accusations against Olly Robbins and reinstate him to the job the country needs him to do.”

The controversy has reignited concerns in Labour’s ranks about the prime minister’s future, with several senior sources saying they believe Starmer is on borrowed time.

One minister described him as being in a “holding pattern”, giving him between 12 and 18 months more in the job. “There isn’t a fundamental shift,” they said. “The bottom line remains the same … A lot depends on Andy [Burnham, one of Starmer’s most likely challengers].”

Another added of the current atmosphere: “It’s weirdly resigned and everyone is sort of gallows humour and depressed. I think it’s just not over and its just a bit terminal.”

The pressure is unlikely to break in the coming days as MPs continue to pick over the decision to appoint Mandelson. On Thursday Cat Little, the lead civil servant at the Cabinet Office, will testify in front of the foreign affairs select committee. She will be followed next Tuesday by Morgan McSweeney, the prime minister’s former chief of staff.