Lib Dems could form coalition with Tories to unseat Labour

Vince Cable, the party's treasury spokesman, says the political "pendulum" may not swing in the Tories' favour because Britain now has a three-party system. In a pamphlet published today by the think-tank Demos, Mr Cable says: "It may now be too late for a party of the right - squeezed between 'cultural conservative' and 'libertarian' forces - to re-emerge as an undisputed voice of opposition. If the pendulum swings, it may swing to a combination of Conservatives and Liberal Democrats and, thus, to a period of minority government or coalition, in some form."

He adds: "A point might well come at which, fearing for their future, Labour or the Conservatives might embrace electoral reform, in which case a different type of future beckons."

Such speculation will be fuelled by a new study by Essex University which forecasts a hung parliament after the next election. Professor Paul Whiteley, co-director of the British Election Study, said: "The next general election will very likely produce a hung parliament with no party having an overall majority, and Gordon Brown is unlikely to change this unless Labour can reinvent itself."

The study found that Labour would have lost its majority if this year's election had been held on 5 April, the day it was called, rather than a month later. "Labour was saved by the fact that the Conservative campaign failed so badly.''