Gordon Brown thought his luck had changed when the shadow home secretary said he was resigning over 42-day detention. Conservatives, by contrast, thought he had gone mad. Yet to judge from the emails sent by Tory activists, Labour voters and people who had never given a thought to politics, the MP for Haltemprice and Howden may be on to something, writes political editor Gaby Hinsliff

When a battle-weary David Davis got off the train home on Friday night, the condemnation of his colleagues ringing in his ears, he headed to his local pub for solace. His aides were waiting, with a sheaf of emails they stuffed straight into his hands.

They came from excited Tory activists, life-long Labour voters, ordinary people who had never written to politicians before: there was an offer of help from a Lib Dem constituency chairman and pledges of cash from pensioners. But one, he admits, gave him 'a lump in the throat': it was from a woman who worked on a local government project to encourage the alienated and unfranchised to vote. What he had done, she wrote, would 'make my job so much easier'.

When one of the most aggressively ambitious men in politics last week threw away the chance of becoming home secretary to embark on what one shadow cabinet colleague describes as an 'utterly barking' crusade for civil liberties, the Westminster verdict across all parties was instant: it was an ego trip, a midlife crisis; at best, a naive romantic whim and, at worst, a selfish plot to destabilise his leader. Even his friends, none of whom had been consulted, were appalled.

But as the dust settles, Davis's eccentric rejection of conventional politics is beginning to pose some awkward questions.

He still risks ridicule if his grand mission flops, but as Iain Dale, the Tory blogger who ran Davis's ill-fated leadership campaign, points out, while newspapers scorned the resignation the blogosphere largely embraced it: political chatrooms are overflowing with right-wingers offering to start a fighting fund, and left-wingers agonising over whether to support him. Even the Daily Telegraph's Saturday letters page was two to one in favour of the former MP for Haltemprice and Howden.

Could David Davis somehow have stumbled across something the establishment has missed, an untapped anger with what the public sees as a snooping, heavy-handed state that spies on it through speed cameras and CCTV and microchips on its rubbish bins, that tramples its freedoms and makes sloppy mistakes with its private data?

'I was hoping it would strike a chord with the public, and it turns out it really has touched a nerve,' Davis told The Observer yesterday. 'The more people from all walks of life who want to join in, the better. We will be looking to get non-politicians involved: I'm pretty sure we will have some senior lawyers.'

With their help, he argues, he will challenge the opinion poll findings suggesting that Britons overwhelmingly support extending detention of terror suspects without charge to 42 days, which have made some politicians afraid to defy the government on the issue. 'We will say, "If you knew that half the people who went to 28 days' detention were innocent, would you support it?" We will do the same with the DNA database, with other issues.'

He hopes to run the campaign on small donations from ordinary people, and stage genuine debates engaging everyone from politicians and those who have directly experienced terrorist violence to ordinary people. It could be, said one aide, an 'Obama-like' campaign for the masses.

Such rhetoric may sound overblown. But yesterday he scored his first serious political hit, as the maverick Labour MP Bob Marshall-Andrews announced he will campaign for Davis.

What was a crisis for David Cameron is now becoming a serious headache for Gordon Brown, who must now decide whether to discipline his rebellious MP and turn him into a dangerous martyr, or ignore him and risk others joining in, turning a by-election that Brown dismissed as a farcical stunt into a cross-party uprising. Is British politics seeing the emergence of something genuinely new? Perhaps.

Sceptical colleagues still believe Davis is playing the oldest game in politics: positioning himself for the leadership should anything befall Cameron. One who knows him well argues that Davis 'basically doesn't approve of the Cameron Project' and has chosen to abandon it: 'I think he thinks this is a bold bid of the type that would have worked for Enoch Powell if the Tories had lost the 1970 election. He's very struck by historical parallels.'

Powell stood for the Tory leadership in 1966 and came a poor third. Two years later his 'rivers of blood' speech abruptly ended his frontbench career but caught a public mood: historians credited Powellite politics with swinging millions of Tory votes in 1970. Four decades on, his voice still echoes in the British immigration debate. Does Davis have something similar in mind?

His friends say Davis would now rather spend his career being his own man than following a leader with whom he increasingly disagrees on issues from environmentalism to tax cuts. 'Does he really want to be Cameron's home secretary? Not much,' says a senior MP who is close to him. 'The most important thing to David is to be a big character.'

Davis himself insists, however, there are no rifts and no hidden agendas: he simply believes he doesn't need a seat at the shadow cabinet table to pursue his cause, insisting that his successor Dominic Grieve - a passionate opponent of detaining terror suspects for 42 days and the only colleague he discussed his plans with - can continue the parliamentary battle without him: 'Dominic is at least as good as me and probably better.'

By Davis's own admission, Grieve has an uphill job. Up until last weekend, Davis believed Brown would be defeated on the terrorism Bill in the Commons and was certain he would be defeated in the Lords. He says he began to think again when he saw last-minute polling suggesting that 65 per cent of the public supported it. As he makes clear for the first time today, he feared Cameron would not be able to hold the libertarian line as it got closer to a general election.

Was he right? Well-placed sources say there were certainly disagreements about how firmly Tory peers should be whipped on the terrorism Bill. Michael Gove and George Osborne, the two shadow cabinet minsters closest to Cameron, also both had broader reservations about appearing soft on terrorism.

Those closest to the discussions insist there was 'never any question' of Cameron doing a U-turn and that he knew, if he had did, frontbench resignations - and not just Davis's - would have followed. Even those who share his concerns argue that Davis should not have quit.

'Cameron has treated David very well and he deserves better,' said one shadow cabinet colleague, who regards Davis as being 'out of his fucking mind' for drawing attention to one of Brown's few popular policies.

The unrepentant Davis, however, argues the terrorism Bill was only part of a jigsaw of controversial issues he wants to debate, which include the estimated one million people whose samples are held on the police DNA database even though they have never been convicted of any crime, and the surveillance powers introduced to combat terrorism being used by councils to enforce anything from school admissions policies to dog fouling.

He said he was not embracing a full libertarian agenda of abolishing CCTV cameras or scrapping the DNA database, but both mechanisms should include stronger protection for innocent citizens: 'I wouldn't say, don't have a DNA database: I would have everybody who has ever been to prison on it, but the innocent get taken off.

'It's the past people we don't have, the people who were imprisoned 10 years ago. That way we would protect the rights of the innocent and we actually solve far more crimes. As for surveillance powers, it cannot ever have been Parliament's intention that there should be a thousand surveillance operations by local government.'

He said he also wanted to see tougher safeguards controlling the use of data from CCTV cameras: 'Most of them are no good for evidence. There should be a requirement that they should be of evidential standard and with that will go a mandatory penalty for misuse of the data. At the moment we've got 3 per cent of crimes solved by surveillance camera, and 80 per cent of cameras are useless in court.'

Such policies may be harder for Labour to attack than it thinks. The government consensus was that Davis had scored what one senior party figure calls 'the biggest own goal in history' - knocking Brown's woes off the front pages, exposing Tory tensions and pitting his party against Rupert Murdoch's Sun, now the leading proponent of 42 days.

Within hours of his resignation, senior Labour aides were suggesting the paper could mount a candidate against him; by Friday morning, ex-Sun editor Kelvin MacKenzie had offered to stand. MacKenzie has said the idea followed a party for Sun editor Rebekah Wade's 40th birthday, attended by Murdoch, on Thursday night. But Wade's inclusion on the guest list for a girlie sleepover hosted by Sarah Brown at Chequers this weekend has only fuelled speculation that Downing Street was closely involved in encouraging the Sun to join the fight.

Is MacKenzie really a Labour puppet? If so, he needs his strings tightening. Within 24 hours, he had committed at least two gaffes, insisting that Murdoch had personally promised to fund him - as an American citizen, Murdoch cannot legally do so - and being caught unawares on camera describing Hull, next to Davis's constituency, as an 'absolute shocker' of a place.

Labour's refusal to say if it will put up a candidate has triggered suspicions that it is seeking a convincing outsider to pit against Davis, with names in the frame including the Glasgow airport baggage handler John Smeaton, who helped to foil an alleged bomb attack there.

The Sun is also said to have considered approaching Rachel North, a survivor of the 7/7 bombings, who has campaigned for justice for the victims, but North said she admired Davis's stand: 'I am a big fan of civil liberties and freedom and democracy, all things that terrorists are not keen on, and I'm pleased that a senior politician has campaigned about this.'

Would she go out on the stump for him? 'I might do something, but he hasn't asked me.' Davis, unsurprisingly, says she is 'exactly the sort of person' he would welcome.

Could all this political party cross-dressing lead towards the emergence of a new political movement, with Davis at its head? Not according to Davis: 'When they cremate me, the ashes will be Conservative.'

If the gamble goes wrong, however, he could be supporting his party from an armchair in Yorkshire, not from inside a future Tory government. But if he pulls it off, Davis may yet inflict more damage on Brown than his nervous colleagues realise. The ball is in Labour's court.