Dominic Raab has said he will resign from Cabinet if a bullying allegation is upheld against him.

The Deputy Prime Minister is being investigated by senior lawyer Adam Tolley KC over claims of bullying – with dozens of officials thought to be involved in eight formal complaints.

Asked about the probe on Sky’s Sophy Ridge On Sunday programme, Mr Raab reiterated to have “behaved professionally throughout” .

He dismissed calls to stand aside while the probe is carried out, insisting “that’s ultimately for the Prime Minister to decide”, adding: “I think, actually, just by lodging complaints, you can knock out a Cabinet minister or senior figure, (I am) not sure that is right.

“We believe in innocent until proven guilty in this country and I’ll co-operate fully with the inquiry, and I’ll respect the outcome of it.”

Asked whether he will then resign if the complaint is upheld, at first, Mr Raab said he was not going to start speculating on what the outcome might be.

When pressed further, he said: “Allow me to respond in the right way at the right time, of course. Look, if an allegation of bullying is upheld, I will resign.”

Making an appearance on the BBC’s Sunday With Laura Kuenssberg programme later on, Mr Raab also faced questions about his conduct.

He denied he is a bully but said he had learned lessons from his dealings with civil servants in the past.

Asked whether he had ever reflected on his dealings with staff and felt he “shouldn’t have reacted in that way”, the Justice Secretary said: “Look, in terms of working style, falling short of any of the impropriety you refer to, look, of course, we learn lessons as we go.

“That is part of the relationship with civil servants. But I’m confident that I’ve behaved professionally throughout.

“I think the lion’s share of the time, the vast majority of cases and the time we spend together, civil servants and ministers work very effectively together.”

On whether there should be “more plain speaking in politics”, he replied: “Yes, absolutely.

“What we need, and I think this can be reconciled absolutely with having a zero tolerance on bullying, you need ministers who come in and correctly but directly challenge assumptions, test ideas — that is the way we get the best out of Government.”

Dave Penman, general secretary of the FDA union, dismissed Mr Raab’s comments, insisting civil servants do not “have the confidence” to challenge bullying or harassment by senior figures in Whitehall.

He told the BBC’s Sunday With Laura Kuenssberg programme: “The picture he paints is that everything is fine in the civil service and the relationship between ministers and civil servants is OK.

“That’s not the picture civil servants speak of, that’s not their experience.

“One in six are saying they have experienced bullying or harassment, or have witnessed that, in the last 12 months alone across 20 Government departments.

“They don’t have the confidence of challenging those behaviours.”

Responding to Mr Raab’s comments about the investigation into bullying allegations against him, Liberal Democrat chief whip Wendy Chamberlain said the Prime Minister “should finally show some backbone” and suspend him while the investigation is ongoing.

She added: “That is what would happen to someone facing such serious allegations in any other workplace. The current position is completely unsustainable, how can crime victims expect justice when the minister responsible is busy trying to clear his own name?”