Dominic Raab is being investigated over five fresh formal complaints about his conduct after Rishi Sunak referred the new allegations to the senior lawyer carrying out a bullying inquiry.

The new claims, which take the total number in Adam Tolley KC’s investigation to eight, are believed to relate to the Deputy Prime Minister’s first stint as Justice Secretary.

Labour and the Liberal Democrats suggested Mr Raab should be suspended, but the Prime Minister’s official spokesman said it is “right” that the inquiry is finished before decisions are made.

Mr Raab has insisted he “behaved professionally at all times”, but the more than doubling of the number of formal complaints is a blow to his attempts to clear his name.

Downing Street said the latest allegations do not relate to Mr Raab’s current tenure at the top of the Ministry of Justice (MoJ), with Mr Raab having been reappointed to the role by Mr Sunak in October.

“I can confirm that the Prime Minister has now asked the investigator to include five further formal complaints relating to conduct at the Ministry of Justice as part of the ongoing investigation and in line with the existing terms of reference,” Mr Sunak’s official spokesman said.

He would not put a timescale on when the investigation into the MP for Esher and Walton in Surrey will be concluded but said it is hoped to be finished “swiftly”.

Asked how Mr Raab can remain in his Cabinet role considering the breadth of the allegations, the spokesman responded: “We think it’s right there is an independent process, that the investigator looks into these claims thoroughly before coming to a view.”

Mr Raab first served as justice secretary under Boris Johnson for a year until September. He was ousted by Liz Truss but Mr Sunak brought him back after he succeeded her as Prime Minister.

He also held jobs at the MoJ between 2015-2016 and 2017-2018, but the new allegations are understood to relate to his first tenure as justice secretary.

One complaint about his conduct in the role was already being investigated, as were two others lodged about his time as foreign secretary and Brexit secretary.

Labour suggested Mr Raab should be suspended while under investigation and urged ministers to ensure that civil servants are safe.

Deputy leader Angela Rayner said: “It is yet another sign of how weak Rishi Sunak is as a Prime Minister that, despite being aware of Dominic Raab’s reputation, he appointed him as his deputy.

“The Prime Minister must now say why he has not been suspended until the outcome of the formal investigation, and make clear that any breach of the Ministerial Code will result in his immediate sacking.

“The Government must also take immediate steps to ensure there is a safe working environment for their staff.”

Lib Dem deputy leader Daisy Cooper said: “The trickle of allegations about Dominic Raab has turned into a flood and his position is becoming increasingly untenable.

“Rishi Sunak must ask Raab to step down as Justice Secretary while these complaints are investigated, and confirm he won’t be reappointed if they are upheld.

“Anything less would make a mockery of Sunak’s claim that he would govern with integrity. It can’t be one rule for Conservative ministers and another for everyone else.”

Dave Penman, general secretary of the FDA union which represents senior civil servants, also raised questions about how Mr Raab can continue in the role.

“Given the volume of complaints, if this was a civil servant – at any level – there’d be a legitimate question of whether they should be suspended pending the investigation,” he said.

The Prime Minister appointed Mr Tolley, a commercial and employment law specialist, to look into two initial formal complaints in November, but this is the second time his inquiry has been expanded.

The lawyer needed to be brought in because the role of adviser on ministers’ interests has been empty since Lord Geidt’s resignation in June.

Downing Street said the process to find a replacement is continuing.