The Conservatives have opened a commanding 13-point lead over Labour, their biggest for 19 years, according to the latest monthly poll by ComRes for The Independent. The survey, taken after Gordon Brown's worst week since becoming Prime Minister, puts the Tories on 40 per cent (down one point on last month), Labour on 27 per cent (down six points), the Liberal Democrats on 18 per cent (up two) and other parties 14 per cent (up four). If repeated at the next election, the figures would give David Cameron an overall majority of 64 seats.
The last survey which showed such a big Tory lead was a MORI poll for The Times in August 1988, when Margaret Thatcher was Prime Minister and her party enjoyed a 14-point advantage.
Labour's slump is bound to be attributed to a backlash over the fiasco in which sensitive personal data about 25 million people was lost by HM Revenue & Customs and doubts over whether taxpayers would recover the £24bn of government-backed loans to the troubled Northern Rock bank.
The only crumb of comfort for Mr Brown is that the Tories do not appear to be reaping the benefit from his mounting problems. There will be disappointment in Conservative circles that the party's rating has slipped by one point since last month. Those abandoning Labour seem to be switching to the Liberal Democrats or other parties.
Labour sources said the poll findings, while gloomy, suggested that the Brown Government was not in the same place as the Tories under John Major after "Black Wednesday" in 1992. From then on, Labour profited directly from the Tories' troubles, soaring ahead in the polls and retaining a big lead until it finally won power at the next election in 1997.
According to ComRes, Tory support remains strongest among men (up from 41 per cent to 43 per cent), but has fallen back among women (down from 41 per cent to 37 per cent).
Mr Brown's nightmare week appears to have alienated men, among whom Labour's ratings have slumped from 31 per cent to 22 per cent. Among women, Labour has dropped from 34 per cent to 31 per cent.
The Tories have slipped among 18- to 24-year-olds but they are otherwise ahead of Labour across all age bands, social groups and regions – except Scotland – including Labour's traditional heartland in the North.
The Tories remain the best at keeping their core vote, with 92 per cent of Tory identifiers saying they intend to vote for the party, compared with 78 per cent of Labour identifiers and 70 per cent of Liberal Democrats
Some 17 per cent of people who regard themselves as natural Liberal Democrats say they would vote Conservative, as would 9 per cent of Labour identifiers.
Mr Cameron's party is the best at getting its supporters out: 72 per cent of them are "absolutely certain" to vote compared with 58 per cent of Liberal Democrat voters and 57 per cent of Labour supporters.
The survey is good news for the Liberal Democrats, suggesting they are continuing their steady climb after slumping to a low of 11 per cent after the resignation of Sir Menzies Campbell last month. Their recovery may be seen as a reaction to the higher media profile they are enjoying during the leadership contest between Nick Clegg and Chris Huhne.
The Liberal Democrat revival is stronger among women, among whom their support has risen from 17 per cent to 20 per cent in the past month, than men, among whom they have risen one point to 16 per cent.
The findings will fuel anxiety among Labour MPs, particularly those representing marginal seats, who are calling on Mr Brown to recover his reputation for competence before it is lost for good.
However, Brown allies will regard the ComRes figures as evidence that the Prime Minister still has time to turn things round. They will say the small drop in Tory support shows the Opposition has not yet developed an alternative agenda for government and that Mr Cameron is not yet seen as a prime minister-in-waiting.