One-third of readers of the Daily Telegraph, long assumed to be true- blue Conservatives, intend to vote Labour at the next general election, the research shows.
Lord McAlpine's view that even a Tory can see that it is time for a change, ridiculed by the Prime Minister in the Commons on Thursday, appears to be echoed in the party's heartlands.
Among readers of the Daily Mail, the Times and the Sunday Times, support for Labour is even higher, at 38 per cent, 39 per cent and 42 per cent respectively. At the Sun, which claimed to be the paper "wot won it" for Mr Major in 1992, the figure is 59 per cent, virtually the same as in the electorate as a whole.
Support for Labour is now so widespread that no daily newspaper has a readership which is more than 50 per cent Conservative. The survey is clear evidence that Tony Blair is attracting floating voters and even lifelong Conservatives in the marginal seats in southern England which are expected to decide the next election.
It also strongly suggests that the right-wing papers' line on Mr Major, which has been largely sceptical for two years or so, is having an increasing impact on readers.
The swing from the Conservatives to Labour since 1992 (given in the final column of our table) is markedly lower at the Daily Express, the one Tory paper that has remained broadly loyal to the Government. At the Mail, the paper that has most in common with the Express in other respects, the swing is 24 per cent; at the Express it is only 18.
"This is jolly interesting," says John Curtice, a psephologist and senior lecturer in politics at the University of Strathclyde. "It's a wonderful natural experiment. The Express and Mail readerships are sociologically very similar. So if there's a difference in their voting intentions, it's something to do with the newspapers, rather than with the readers. It shows that, yes, newspapers have an effect."
The survey has unusual authority as it is a "poll of polls". Whenever MORI conducts a poll of voting intentions, it includes a question about newspaper-reading habits. These latest figures are the combined results of all polls carried out in the last quarter of last year, with a total sample of 10,986 people. (Non-voters, don't-knows, and won't-says are excluded.) They were therefore collated before the recent changes to Labour's Clause IV, which are likely to have won further support for Mr Blair.
The figures for the Daily Telegraph are perhaps the most striking. It is not just the paper's traditional stance that makes its readers a vital constituency for the Conservatives; it is the fact that there are so many of them.
At 1,057,777, the paper's circulation is much the highest among the daily broadsheets, some 430,000 ahead of its nearest rival, the Times. With each copy read by up to three people, MORI's figure of 33 per cent represents something like a million votes for Labour.
The Telegraph readers' drift to Labour has happened gradually over the past year. Support for the Conservatives has slipped only slightly, from 52 per cent in the first quarter of 1994 to 48 in the last quarter. But support for Labour has risen sharply, from 23 per cent early in the year, to 28 per cent in the summer, to 33 per cent in the winter. The Lib Dems' share of Telegraph readers fell from 26 to 16 per cent in the second half of last year.