Conservative MPs have ramped up pressure on Boris Johnson to dispense with his top aide amid fresh allegations that Dominic Cummings broke lockdown rules more than once.

The Prime Minister has been urged to sack Mr Cummings after reports surfaced that the 48-year-old made a second trip to County Durham, where his family lives, despite stringent social restrictions being in place.

Backbench Tories, including prominent 1922 Committee member Steve Baker, said Mr Cummings “must go”, but the senior Government adviser has denied the fresh allegations that he returned to Durham in April, weeks after his initial time spent self-isolating in the region.

Speaking outside his London home on Sunday, after one journalist asked if he had been back to Durham in April, Mr Cummings said: “No, I did not.”

He then made his way to Number 10.

The PM pledged his “full support” on Saturday to his under-fire chief adviser, who it emerged had travelled 260 miles to the North East in March to self-isolate with his family while official guidelines warned against long-distance journeys.

According to the Sunday Times, the Tory leader told allies he would not throw Mr Cummings “to the dogs” following reports he made the journey to ensure his four-year-old child could be looked after as he and his wife were ill.

But according to reports in the Observer and Sunday Mirror, the former Vote Leave campaign co-ordinator made a second trip to Durham and was seen there on April 19 – five days after being photographed on his return to Westminster.

A second witness told the papers they saw him a week earlier in Barnard Castle on Easter Sunday, a popular tourist location 30 miles from Durham, during the period he was believed to be self-isolating.

Downing Street has said it would “not waste time” replying to the fresh allegations from “campaigning newspapers”.

But Mr Baker told Sky’s Sophy Ridge On Sunday programme: “If he doesn’t resign, we’ll just keep burning through Boris’s political capital at a rate we can ill afford in the midst of this crisis.

“It is very clear that Dominic travelled when everybody else understood Dominic’s slogans to mean ‘stay at home, protect the NHS and save lives’.”

Craig Whittaker, Conservative MP for Calder Valley in West Yorkshire, said Mr Cummings’ position was “untenable”.

He tweeted: “You cannot advise the nation one thing then do the opposite.”

Transport Secretary Grant Shapps, who was sent out to defend Mr Cummings at the daily Downing Street coronavirus briefing on Saturday, faced questioning on the adviser’s actions on Sunday but admitted he had not spoken to him beforehand.

The Cabinet minister, in an interview on the BBC’s Andrew Marr programme, said Mr Cummings was not going to resign.

He also said: “I’m afraid I don’t know (about Barnard Castle) but if that date was true that would have been outside the 14-day period. But I’m afraid I don’t have the information on that.

“But I do know it is not the case that he has travelled backwards and forwards, which seemed to be a major part of the stories I saw in the paper today.”

Pressed by the BBC’s Andrew Marr on whether there was an “extreme risk to life”, Mr Shapps added: “A four-year-old can’t feed themselves, a four-year-old can’t bathe themselves and change their clothes, so it is clear they wanted to put some measures in place.”

On Saturday, deputy chief medical officer Jenny Harries said everyone should self-isolate unless there was a risk to life.

Labour said if everybody in the country had followed Mr Cummings’ example, the rate of transmission of coronavirus would not have slowed.

Shadow policing minister Sarah Jones told Sophy Ridge: “If everybody had decided to break the rules then we wouldn’t have brought this infection rate down.

“And when we heard the Prime Minister, we heard him say ‘stay at home, protect the NHS, save lives’ – he didn’t say ‘or drive 260 miles to Durham if you think that’s the right thing to do’.”

The party has called for Mr Johnson to front the daily Downing Street press conference to explain what went on and is also demanding an investigation into Mr Cummings’ behaviour.