Deputy Labour leader Harriet Harman also insisted the by-election – which could cost up to £80,000 or even more of public money – was “not necessary” and that it was about divisions among Conservatives.

Mr Davis denied a split or that he was undermining David Cameron, who beat him to the leadership in 2005. 

“On the issue of substance, there is not a cigarette paper between us,’’ Mr Davis said.

Mr Cameron pledged to campaign for Mr Davis but was not consulted and is said to have been angered.

He acted swiftly to find a new Shadow Home Secretary and is being urged to go for a full-scale reshuffle.

Mr Davis denied being on an “ego trip’’ or that he was suffering a mid-life crisis – but conceded his frontbench career may be over.

He hailed positive reactions from the public, including “thousands’’ of congratulatory emails and support from contributors to the Conservative Home Tory website, whose poll suggested 65 per cent of members were “inspired’’ by his move.

But comments on the site yesterday also included sharp criticism.

Senior Tory MP Sir Patrick Cormack said: “The party won the argument and as one of my Northern Ireland colleagues said, it was a humiliating victory for Mr Brown. Now all the attention is taken off that.’’

Frontbencher Chris Grayling said that Mr Davis was “a man of principle fighting on the issues that we know he cares about” adding: “Whether I would have chosen in his position to do exactly the same thing, I don’t know. But he’s taken a courageous decision. I think we should back him.”

Mr Davis may find that his main rival is Kelvin MacKenzie, former editor of The Sun, who said he was “90 per cent certain” to stand if Labour did not.

However, he was embarrassed when caught on microphone describing nearby Hull as “an absolute shocker”. He later said he had been joking and had never been there.

The Monster Raving Loony Party is taking part with a candidate called Madcow.

The campaign is poised to start next week with July 10 the likely poll date.