A growing number of Conservative MPs have voiced their frustration over Dominic Cummings after he said that he had “no regrets” about his trip to Durham.

In a press conference on Sunday, Mr Cummings – Boris Johnson’s chief adviser – defended a 260-mile trip from London to the north-east of England he made with his family during lockdown, explaining that he believes he behaved “reasonably”.

However on Tuesday, Douglas Ross, the parliamentary under-secretary of state for Scotland, quit the Government, saying that he could not “in good faith” defend Mr Cummings’ actions.

Speaking in an interview with the BBC, Mr Ross said that there are still unanswered questions regarding the actions of Mr Cummings.

On his decision to quit his role, he said: “Well it’s a personal decision. I can only be accountable for my own decisions and as I’ve said, this is not unanimous.”

Mr Ross added: “I think there are still unanswered questions with his (Mr Cummings) statement and that’s why I felt I couldn’t go out and defend it.”

At least 24 Tory MPs have now spoken out against the actions of Mr Cummings, including veteran Sir Roger Gale who said that the Conservative backbench 1922 Committee should make it clear to the PM that his adviser should go.

“The time I think has come for Mr Cummings to resign or for the PM to dispense of his services,” Sir Roger said.

The North Thanet MP told the PA news agency: “There are people on the 1922 executive who are courageous, and that’s their job.

“They are elected to tell the PM what he needs to hear, not what he wants to hear.”

Senior Tory William Wragg, chairman of the Public Administration and Constitutional Affairs Committee in the Commons, said that it was “humiliating and degrading” to see ministers put out agreed lines in defence of Mr Cummings, while Caroline Nokes, chairwoman of the Commons women and equalities committee, said she had informed her party whips there could not be “wriggle room” for some people when it comes to lockdown rules.

Former health secretary Jeremy Hunt said he believed Dominic Cummings broke lockdown rules on multiple occasions, but added that he was not calling for the Prime Minister’s adviser to resign.

In a letter sent to constituents, Mr Hunt wrote: “Having watched the broadcast yesterday, my own view is that what he did was a clear breach of the lockdown rules – coming back into work when he had been with his wife who was ill, driving to Durham instead of staying at home and visiting Barnard Castle.

“These were clearly mistakes – both in terms of the guidance which was crystal clear, and in terms of the signal it would potentially give out to others as someone who was at the centre of government.”

He added: “But as someone who has been at the centre of media storms with a young family I know you do make mistakes in these situations. I have made them myself. So I am afraid I am not going to add my voice to the list of those calling for him to resign.”

Meanwhile, County Durham’s three Conservative MPs issued a joint statement saying Mr Cummings’ public statement had addressed “a number of concerns”.

“Overall, we believe his actions to be motivated out of his desire as a parent to do what he thought was necessary in protecting his family,” the statement from Richard Holden, who represents North West Durham, Bishop Auckland MP Dehenna Davison, whose constituency includes Barnard Castle, and Paul Howell, who represents Sedgefield, said.

“However, in the same circumstances, none of us would have made the decisions he made – particularly over the visit to Barnard Castle. We also closely followed the statements from Durham Constabulary as they clarified what had happened.

“It is our collective view that, above all else, this continuing situation is creating a major distraction from the vital work of the Government as it leads our country in combating the global coronavirus pandemic.”

Conservative MP for Rugby Mark Pawsey said that Mr Cummings had “acted very much against the spirit of the lockdown rules” and should be sacked, while Conservative former chief whip Mark Harper also said he believes Mr Cummings should have offered his resignation to the Prime Minister.

He said he would “expect an adviser who had damaged the credibility of the Government’s central message so badly and had become the story to consider their position”.

Former minister Stephen Hammond said his concern was “the distraction this is causing at a time of national crisis and the way it is undermining confidence in the public health message”.

“Public adherence to the rules is achieved by consent in this country and that is made much harder if people feel it is one rule for them and another for senior Government advisers,” he added.

In a statement on social media, the Conservative MP for Eastleigh Paul Holmes said that the Government’s handling of the situation had not been its “finest hour”.

And Conservative former minister Robert Goodwill has also called for Mr Johnson to sack Mr Cummings.

The Scarborough and Whitby MP told the PA news agency: “I’ve been contacted by over 400 constituents who, with one or two exceptions, have been critical of Mr Cummings, and his statement yesterday has done nothing to convince them otherwise.

“I think that the best way for the Prime Minister, who I’m a massive fan of, to show he’s in charge of the situation is to relieve himself of Mr Cummings’s services.”

Speaking to STV News, Scottish Conservative leader Jackson Carlaw said that Mr Cummings should now be considering his position.

Mr Carlaw said: “Given the furore, given the distraction this is, given the distraction of the Prime Minister on this issue, if I were Mr Cummings I would be considering my position.”