A third complaint against Dominic Raab is being investigated by the probe ordered by No 10, deepening the crisis surrounding the deputy prime minister.
The inquiry into Rishi Sunak’s key ally was already looking into his behaviour while justice secretary and Cabinet Office minister – but his time as Brexit secretary is now also under scrutiny.
A Downing Street spokeswoman said the third compaint was received two days ago, adding: “The prime minister has asked for that to be looked into.”
A leading lawyer, Adam Tolley, was appointed this week to investigate whether Mr Raab was guilty of bullying, or other unacceptable behaviour, in his previous roles.
It has always been possible for the inquiry to be widened, amid a blizzard of further allegations from senior civil servants in several government departments.
BBC Newsnight reported this week that the deputy prime minister’s former private secretaries, responsible for his day-to-day affairs, were preparing to submit formal complaints.
Mr Sunak – desperate to avoid losing a second minister to bullying claims, after the departure of Gavin Williamson – has continued to express “full confidence” in Mr Raab.
But No 10 said the third formal complaint was received by the Cabinet Office on 23 November, leading to a widening of the scope of the inquiry.
“The prime minister has now asked the investigator to add a further formal complaint relating to conduct at the Department for Exiting the European Union and to establish the facts in line with the existing terms of reference,” the spokeswoman said.
Dave Penman, the general secretary of the FDA civil servants’ union, has described the allegations against Mr Raab as “an extraordinary set of circumstances”.
“We’ve never come across a situation where so many civil servants appear to be raising complaints about a minister’s conduct,” he said.
“There are a series of allegations that appear to be coming across a number of departments where Dominic Raab has worked. Each one is going to have to be approved by the prime minister for investigation.”
The deputy prime minister, who requested the Tolley investigation, has denied any wrongdoing, telling Sky News on Thursday: “I have behaved professionally at all times.
“I am the one that, when the complaint came in a matter of days ago – the first that had ever come against me since I have been a minister since 2015 – called for an independent inquiry.
“I look forward to dealing with it fully and transparently, rather than dealing with anonymous comments in the media.”
Mr Raab also denied he broke the ministerial code by using his private phone for official communications, as reported.
“I have always adhered to the ministerial code, including the use of my iPhone,” he insisted, adding he had “always been careful to protect the integrity of any communications”.