The Conservatives last won a general election in 1992. That was also the year when the opinion polls met their Waterloo. The results of 50 nationwide surveys were published during that campaign. All but six showed Labour ahead, and they all suggested that the outcome of the election would be a hung Parliament, with Labour probably the largest party. They were all wrong. The largest Tory lead reported by any poll during the campaign was only a single percentage point. In the event, the Conservatives’ lead over Labour approached eight points.

To this day, no one knows why the polls came a cropper in 1992. Indeed, no one knows for sure why the polls went on to perform with only indifferent success in 1997 and 2001. To be sure, they forecast comfortable Labour victories on both occasions, but most of them — as in 1992 — exaggerated Labour’s share of the vote. Only last time, in May 2005, were the poll forecasts in line with what actually happened.

The obvious inference to be drawn is that, even now, opinion-poll findings may not be entirely reliable. Maybe the Tories are not as far ahead as they seem. There is, however, a less obvious inference to be drawn: that anyone wanting to know what is really going on should not rely too heavily on the headline voting-intention figures.

Even in 1992 there were signs that all was not as it seemed — signs that caused some of us at the Daily Telegraph to counsel against the paper’s organising its post-election coverage on the assumption that Labour, not the Tories, had won.

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For example, although some (not all) of Gallup’s surveys for the Telegraph showed Labour ahead, the responses to the same organisation’s principal question on the economy told a different story. Gallup asked: ‘With Britain in economic difficulties, which party do you think could handle the problem best, the Conservatives or Labour?’ On the eve of the 1992 election — at a time when economic issues were uppermost in people’s minds — 43 per cent of those interviewed said the Conservatives, only 31 per cent Labour. Those numbers hardly foretold a Labour triumph. Similarly, if you dug deeper, you noticed that people who responded ‘Don’t know’ to Gallup’s voting-intention question often gave pro-Tory responses to other questions — on who, for example, would make the best Prime Minister (Major, not Kinnock). Perhaps all along there were thousands of bashful or half-hearted Tories out there. They knew or suspected how they would vote but, in the climate of that time, were reluctant to say so.

What about now? Last week YouGov on behalf of the Daily Telegraph presented its respondents with a list of 19 ‘problems facing the country’ and asked which political party they thought could best handle each of them. The problems ranged from the credit crunch through education to Britain’s relations with Europe — and on 18 of the 19 the Tories were ahead. The only exception, bizarrely in view of the Tories’ focus on the issue, was childcare and support for the family. Otherwise the Tories’ leads ranged from a healthy 25 points on traditional Conservative issues such as immigration and law and order to only a single point on the NHS, a traditional Labour issue. The Tories are also well ahead — by 17 points — on economic competence, with Liberal Democrat supporters increasingly leaning in their direction.

There is thus substantial depth at the moment in voters’ preference for the Conservatives over Labour. Even more significant is the fact that, when YouGov asked virtually identical questions on the eve of the general election two years ago, Labour led on most issues (except, as usual, on immigration and law and order). On the economy at that time, Labour’s lead was a comfortable 21 points — compared with the Conservatives’ lead of 17 points now.

However, one feature of YouGov’s latest findings casts a shadow over all the main parties and, indeed, over Britain’s entire political class. It captures a growing trend, one that has scarcely been noticed.

When people are asked YouGov’s ‘best to handle’ question, they are given the option of refusing to name any political party but of responding either ‘None of them’ or else ‘Don’t know’; and the number of people ticking one or other of those boxes has soared in recent months. Last week respondents were asked to say which party they preferred on 19 issues, and the proportion ticking either ‘None of them’ or ‘Don’t know’ fell only once below a third. In nine instances it rose to 40 per cent or more. The cynics and the quizzical together almost invariably outnumbered those opting for any one party. Similarly, asked last week to say who would make the best Prime Minister, 34 per cent said David Cameron (compared with only 16 per cent Gordon Brown), but 40 per cent said ‘Don’t know’ — a far larger proportion than was ever recorded in the past.

Under present circumstances, a popular vote of confidence in Britain’s entire political class would probably be lost, possibly by a wide margin. Politicians, like bankers, short-sellers and hedge-fund managers, need to attend to their collective reputation.

Anthony King is professor of government at Essex University and a contributing editor to The Spectator.

This article first appeared in the print edition of The Spectator magazine, dated