Tory maverick David Davis yesterday received an unexpected boost in his one-man campaign to preserve civil liberties as rebel Labour MPs announced that they were ready to support him.

The MPs, who are risking expulsion from Labour, may yet turn Davis’s campaign into a problem for Gordon Brown, the prime minister.

Davis unexpectedly resigned last week as shadow home secretary to force a by-election and campaign against the “slow strangulation” of civil liberties. He was spurred to do so after the House of Commons voted to allow police to detain suspects for up to 42 days without charge.

Davis faces continued criticism from fellow Conservatives for his action, with one MP publicly accusing him of “folly and vanity”. However, Bob Marshall-Andrews, Labour MP for Medway and a leading critic of Brown’s terrorism legislation, said yesterday that he would travel to Davis’s Yorkshire constituency to lend his support.

“I applaud David Davis’s decision to resign and fight a by-election on the single issue of civil liberty,” said Marshall-Andrews.

The MP criticised the Labour leadership for its decision not to field a candidate to fight Davis and added: “The election will obviously transcend party politics and I have written to David Davis to inform him that I will be happy to accept any invitation to speak during the course of his campaign to ensure that the voice of a substantial part of the Labour party may be heard.”

Ian Gibson, Labour MP for Norwich North, said: “Davis has a good argument. You can call it a stunt or a gimmick, but there is a serious side to this. I’m quite happy to join in. I’d be quite happy to share that platform to talk about what I think.”

Any Labour MP who actively supports a candidate from a rival party in an election would be guilty of a serious breach of party rules. The normal penalty is the withdrawal of the party whip.

However, Davis’s Tory colleagues continue to voice scepticism about his move, which was privately opposed by David Cameron, the party leader.

Nicholas Soames, Tory MP for Mid Sussex and a close ally of Cameron, said: “It is a disaster for David personally. Words cannot express how foolish he has been.”

Soames added that Davis had let down his party. “Politics is at all times a team game,” he said. “Reliability is all in politics.”

Although other Conservative MPs have expressed private anger at Davis’s resignation, Soames is the first senior party figure to attack him so bluntly in public.

This weekend there was still puzzlement over why Davis had abandoned the chance of becoming home secretary in a future Cameron government. In modern politics, there is no precedent for a sitting MP to quit his seat voluntarily in the middle of a parliament in order to fight to regain it at a by-election.

A member of Cameron’s inner circle claimed that Davis, who has a reputation for intrigue against successive Conservative leaders, had not been motivated solely by his passion for civil liberties. “This is an ego trip and a sure sign that he still thinks he can become leader,” he said.

Davis, who was runner-up to Cameron in the 2005 leadership contest, strongly denies any intrigue. “I categorically will not be leader,” he said. “Absolutely not.”

Asked whether he would stand as leader if invited to do so in the event of a Tory defeat at the next general election, he said: “It begins to sound silly and over the top, but it’s categorically no.”

Davis, 59, a normally gossipy former SAS reservist, conceived his plan in total secrecy. Until Wednesday evening, only two people knew what he might do if Brown won the terror vote: Dominic Raab, his chief of staff, and his wife Doreen, whom he told last Sunday evening.

“My wife always thinks I’m bonkers,” he said afterwards. “I said, ‘You know this might happen?’ She looked at me and smiled and said, ‘Are you sure?’

“Doreen knows exactly how to control me. So we said goodbye and she said good luck.”

Not even his closest political friends were consulted, including Andrew Mitchell, the shadow international development secretary who was campaign manager for Davis’s 2005 leadership campaign.

Davis told Cameron of his plans after Wednesday’s Commons vote. The Tory leader tried unsuccessfully to talk him out of his risky venture.

That evening the Conservative leader hosted a champagne and lychee juice reception for City donors in the back garden of his North Kensington home. Guests later remarked that Cameron had given no impression of a man waiting for a political bomb to drop.

There have been claims that Davis had clashed with Cameron over the Tory opposition to Brown’s plans on 42-day detention. Both sides insist there was no dispute.

Davis may have felt threatened by key figures around Cameron such as George Osborne, the shadow chancellor, and Michael Gove, the schools spokesman, who were concerned about the Conservatives appearing to be soft on terrorism. Recently Davis confided to an opposition MP that he was having trouble with “guys who want my job”.

While Cameron has given a guarded public blessing to Davis’s venture, there will be no financial support from Conservative headquarters for the by-election campaign.

Davis insists that he does not need party money: “We have had thousands of calls of support, right down to the pensioner who says ‘my pension comes in tomorrow. I’ll send some money to Mr Davis out of it’. The offers of money have gone from a fiver to £25,000.”

Some observers have linked his gamble to personal stress or a midlife crisis. One commentator blamed his grand-standing antics on “psychological flaws” traceable to his tough upbringing on a south London council estate. The suggestion was that he was compensating for feelings of rejection when his mother, a single parent, acquired a new boyfriend whom he hated.

Davis yesterday hit back: “That is Westminster village nonsense. If people can’t understand a thing, they make it up. What’s interesting is the distinction between the Westminster village, where you get convoluted analyses, and what’s happening out in the world at large.”

Tomorrow Patrick McLoughlin, the Conservative chief whip, is expected to formally start the by-election process. The vote in Davis’s Haltemprice & Howden seat will take place on July 10.

Whether Davis faces a serious challenger remains to be seen. The Liberal Democrats, who came second in 2005, will not put up a candidate, nor will Labour. Its candidate in 2005, Edward Hart, is reported to have been privately opposed to Brown’s terror legislation.

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