An investigation into claims about Dominic Raab's conduct has been expanded to include a third formal complaint, Downing Street said.
The Deputy Prime Minister and Justice Secretary has repeatedly defended himself against allegations of bullying and using his personal email for government business as Rishi Sunak continued to back him.
Raab said he had always adhered to the ministerial code and "behaved professionally" as fresh bullying claims emerged.
Confirming the scope had been expanded a No 10 spokeswoman said: "I can confirm that 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 third formal complaint was received by the Cabinet Office on November 23, the spokeswoman said. She said the Prime Minister retains confidence in his deputy.
Raab told the BBC: "I've behaved professionally at all times and I'm the one that when the complaint came in a matter of days ago, the first that has come against me since I've been a minister since 2015, called for an independent inquiry and I look forward to dealing with it fully and transparently rather than dealing with anonymous comments in the media.
"I always adhere to the ministerial code, including my use of my iPhone. I've always taken advice on the right means, particularly as foreign secretary and dealing with a whole range of sensitive issues, always been very careful to protect the integrity of any communications I have."
Liberal Democrat chief whip and MP for North East Fife Wendy Chamberlain demanded an investigation after it also emerged Raab had used his personal email account for Government business.
Allies of the Justice Secretary insisted there were no breaches of the ministerial code because he copied in an appropriate Government email address when required by the guidance.
They also argued he was using his personal account just to approve tweets and quotes with his team at short notice.
But Chamberlain said: "The public deserve answers, not more cover-ups. The Deputy Prime Minister cannot be relaxed about national security especially at a time when Britain's enemies are stepping up their cyber attacks.
"It is only right and proper the Cabinet Office investigate these reports and determine immediately if overseas enemies could have seen national secrets sent by Dominic Raab."
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