John Curtice: Crewe is not just an isolated case

It is easy to exaggerate the significance of individual by-election results. The Liberal Democrat victory in Dunfermline two years ago did not herald the party's revival under Sir Menzies Campbell. The 21-point swing to Labour in Mid-Staffordshire in 1990 was not followed by a Neil Kinnock victory in 1992.

But Crewe is not an isolated pointer. It is the latest addition to a jigsaw that portrays a uniformly bleak picture for Labour. In recent weeks the polls have been putting the Conservatives on average 18 points ahead of Labour, a lead reminiscent of those enjoyed by Labour before its landslide victory in 1997. Three weeks ago Labour recorded its worst local election performance for 40 years, trailing the Conservatives by as much as 20 points.

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Now the voters have given the Conservatives a 19 point lead. The tide flowed more firmly in the Conservative direction in Crewe than in any parliamentary by-election since the late 1970s.

The last time the Conservatives secured a 17.6 per cent swing from Labour, as in Crewe, was in March 1977 when Margaret Thatcher snatched Birmingham Stechford from Jim Callaghan's government. In the late Sixties Harold Wilson often suffered heavy by-election losses. As Gordon Brown is now, those Labour governments faced a chill economic wind. Harold Wilson and Jim Callaghan suffered defeat at the next general election. The precedents are ominous.

Statistically, losses of support in Brent East and Leicester South in the last parliament were greater than an 18 point drop, yet Labour still won the 2005 election. But it was the Liberal Democrats who benefited from Labour's unpopularity, not the Conservatives. A Tory revival could cost Labour office.

At the heart of Labour's electoral crisis is a lack of confidence in the Government's ability to handle problems. Mr Brown's personal ratings are in freefall. But the public may not simply be unsure about his ability to steer the country; they may no longer want to go in the same direction.

Unpublished data from the National Centre for Social Research show that just over a third now say the Government should increase taxes to improve public services, the lowest level of support for tax increases since the Eighties. In an era of rising prices, voters seem ready to warm to promises of tax cuts. It is hardly a promising climate for a fourth Labour victory.

John Curtice is professor of politics, Strathclyde University