The vote is seen as a major test of Prime Minister Gordon Brown's popularity and David Cameron's ability to reach out beyond the Conservative heartlands.

Mr Cameron pledged to "pull out all the stops" to secure the seat and opinion polls suggest his party is on course for its first by-election gain in 25 years.

When the campaign was launched 15 days ago, Mr Cameron called for the vote to be a referendum on the Mr Brown's performance since he moved to Number 10 and the 10p tax row.

Labour, defending a 7,780 majority, has rolled out a string of cabinet ministers including Jacqui Smith, Alan Johnson and Jack Straw to charm the voters.

Environment Secretary Hilary Benn and Harriet Harman, Labour's deputy leader, will be in Cheshire, phone canvassing for candidate Tamsin Dunwoody. A party spokesman said the big-hitters would not be taking part in any public events.

Mrs Dunwoody will later go door knocking with actor and supporter John Middleton, who plays the Reverend Ashley Thomas in ITV soap Emmerdale.

Edward Timpson, the Conservative candidate, will visit Nantwich police station with Shadow Home Secretary David Davis.

Liberal Democrat leader Nick Clegg, and his candidate Elizabeth Shenton, will spend the afternoon talking to voters in Nantwich town centre.

The by-election was triggered by the death of 77-year-old Labour veteran Gwyneth Dunwoody last month.