Fathoming the contradictions of what the people want is a nightmare for politicians. Of course a conviction politician doesn't need to know. Present your beliefs and marshal your arguments accordingly, and the people will vote for you if they agree and against you if they disagree. In the olden days, from 1945 up to the Thatcher period, it was relatively straight-forward. Socialism versus capitalism; public versus private; rich against poor; red versus blue.

Tribal politics dictated the policies and the supporters. Add in an occasional reaction against the Government of the day, usually because of a fall in the standard of living, and just enough of the rich, or poor, would switch their votes in protest against the Government to deliver the opposition of the day into power.

Thatcher and Blair changed all that by extraordinary political cross-dressing, thus making old easy choices far more confusing for the modern voter. Essex man, (and Scunthorpe steelworker) who usually voted Labour for most of the years after the Second World War – even during periods of Tory administrations – was suddenly seduced by Thatcher's Tories. Sales of council houses, popular capitalism, lower taxes and control of unions meant there was an army of new Tories who'd broken loose from their traditional Labour moorings.

Similarly, Blair offered former middle-class Tory voters an opportunity of benefiting from Labour governments now worshipping at the altar of capitalist greed, while overlaying the appeal with a deal supposed to offer choice in the provision of public services. Blair successfully cut the moorings between the Tory Party and many of its natural supporters.

But now confusion reigns among voters as the political parties crowd on to the middle ground, offering more or less identical objectives without any ideological base. They're all capitalists but believe in public service provision for health and education. They're all against high taxation. They're all in favour of law and order. And they're all green now. One thing, however, rarely changes (except in 1992). A governing party can only remain in office so long as there is a benign economy. The defeat of the Tories in 1997, notwithstanding the economic recovery of the three years before that election, was ultimately down to the recession of the early 1990s. And the likely defeat of this government in 2010 will be principally because of the financial pain that voters are currently experiencing – and will continue to feel even more during 2009 – when unemployment, inflation, a housing slump and reduced living standards will wreck Gordon Brown's claim to have ended "boom and bust".

David Cameron will be elected to power in spite of, rather than because of, what the Tories have to offer. Indeed, the less he offers, the bigger may be his majority. Therein ,of course, may lie the seeds of his own eventual demise.

David Davis's mid-term gesture – leaving aside where it will leave him personally and politically – certainly appears to have struck a chord with voters beyond the "Westminster village" because it seeks to appeal to the anti-politician sentiment at a time when party ideologies have become blurred. It might also at least resolve the conundrum of whether the polls are right about the public being in favour of 42-day detention. If, as seems likely, Mr Davis storms back to the Commons on 10 July, he will have thrown confusion into the engine rooms of both main parties, currently ruled by the focus groups and the opinion polls.

The real lesson may be that the public is more willing to take from politicians, as individuals, apparently unpopular policies that they won't take from politicians collectively as political parties. Put up a policy, as an individual, in favour of higher taxes on polluting aircraft, or call for more nuclear power or road pricing, carefully argued in isolation, and it may now actually get support at the polls. But put it in a party manifesto and all hell might break loose. And it was this same individualism that probably accounted for Boris Johnson's win in London last month. Standing largely aside from his party label, he captured the anti-politician mood Mr Davis hopes to capitalise on next month. The era of Blair triangulation – "what time is it? what time would you like it to be?" – is over.

Stand for conviction and, even if voters don't agree, they may now be willing to give you a vote. That is the message that Haltemprice and Howden may be sending to Westminster – and David Cameron – next month. Independents have rarely prospered in politics but, even with a party label, Mr Davis may have unwittingly given independents fresh hope in breaking the Westminster mould. Ideology and conviction politics may be back: the third way is certainly over. Mr Davis may be seeing something the rest of us at Westminster are missing.

mrbrown@talktalk.net