Dominic Raab was forced to quit as the UK’s deputy prime minister on Friday, furiously denying he was a bully and claiming “activist” civil servants were targeting him and trying to frustrate government policy.

Raab resigned after an independent report into allegations of his treatment of civil servants upheld bullying claims and Prime Minister Rishi Sunak concluded that his deputy would have to go.

The departure of Raab is a serious blow to Sunak, who appointed his close ally as deputy prime minister last October despite the allegations swirling in Whitehall about his conduct.

Raab said he wanted to “keep his word” to step down if the report commissioned by Sunak found proof of any bullying of civil servants, but he insisted the bar for such a verdict had been set too low.

He blamed “a small minority of very activist civil servants, with a passive-aggressive culture” of trying to thwart him on issues ranging from Brexit to human rights reform. “That’s not democratic,” he told the BBC.

Sunak had agonised for 24 hours over whether the report by Adam Tolley KC, a leading employment lawyer, was sufficiently damning to merit Raab’s removal but concluded in the end there was no choice.

Tolley, who spent five months investigating eight formal complaints against Raab involving allegations by more than 20 officials at three Whitehall departments, upheld two serious claims.

“Because Dom had said he would go if the report came out against him, we were left in a position where there was no other outcome,” said one ally of Sunak.

Oliver Dowden, the Cabinet Office minister and another Sunak loyalist, will succeed Raab as deputy prime minister in a limited cabinet reshuffle. Dowden, a former Remainer, is seen as a technocratic political fixer like his boss.

Alex Chalk, the minister for defence procurement and a barrister, took on Raab’s role of justice secretary.

Opposition parties said Raab’s resignation called into question Sunak’s judgment. Nadhim Zahawi and Sir Gavin Williamson had previously been forced out of the premier’s top team over their conduct.

Despite apologising for any accidental distress he had caused, Raab argued that Tolley had not upheld most of the claims against him, and that the two adverse findings against him were “flawed and set a dangerous precedent for the conduct of good government”.

“Mr Tolley concluded that I had not once, in four-and-a-half years, sworn or shouted at anyone, let alone thrown anything or otherwise physically intimidated anyone, nor intentionally sought to belittle anyone,” Raab said.

In his report, Tolley identified an occasion when Raab acted “in a way which was intimidating” and said his conduct had “also involved an abuse or misuse of power that undermines or humiliates”.

Tolley noted that Raab had been warned his conduct was causing distress to staff by two civil service permanent secretaries and had therefore had an opportunity to change his behaviour.

The former deputy prime minister left open the possibility his departure from the cabinet could herald a decision to leave politics altogether at the next election.

He said he would “let the dust settle” before deciding whether to contest his Esher and Walton seat in Surrey. Raab, who won the seat with a majority of just over 2,700 at the last election in 2019, is facing a strong challenge from the Liberal Democrats.