North Yorkshire MP Rishi Sunak has formally entered the Tory leadership contest, promising he would lead with "integrity, professionalism and accountability" in an apparent attempt to contrast himself with his predecessors as his backers warned a Boris Johnson comeback would be a "guaranteed disaster".

Mr Johnson's supporters have downplayed the fact he is lagging behind his former chancellor in public support from MPs, saying he is "clearly" running, although he has not officially declared this.

Mr Sunak, becoming the second candidate to enter the race after Penny Mordaunt, said he wants to "fix our economy, unite our party and deliver for our country".

He said in a statement: "I served as your chancellor, helping to steer our economy through the toughest of times.

"The challenges we face now are even greater.

"But the opportunities, if we make the right choice, are phenomenal.

"I have the track record of delivery, a clear plan to fix the biggest problems we face and I will deliver on the promise of the 2019 manifesto.

"There will be integrity, professionalism and accountability at every level of the government I lead and I will work day in and day out to get the job done."

Mr Sunak on Sunday gained the back of Northern Ireland minister Steve Baker, an influential figure on the Tory right as the former head of backbench Brexiteers.

Business secretary Jacob Rees-Mogg told the BBC's Sunday With Laura Kuenssberg programme: "I have been speaking to Boris Johnson, and clearly he's going to stand, there's a great deal of support for him."

It came as Nadhim Zahawi, the Chancellor of the Duchy of Lancaster, became Mr Johnson's latest Cabinet backer as he said he "got the big calls rit" and argued "Britain needs him back".