Dateline Thirsk: First big test for the coalition

Candidates for both parties are battling each other for the rural North Yorkshire seat, formed from the former Ryedale and Vale of York constituencies after boundary changes.

The Tories enjoy a large notional majority with Labour needing a swing of more than 14% to oust them and the Lib Dems requiring a 16%-plus switch.

Conservative candidate Anne McIntosh held Vale of York with a majority of 13,712 at the 2005 General Election.

A previous Thirsk and Malton constituency was a Tory stronghold until 1983 when it was abolished.

The Lib Dems could take encouragement from the 1986 Ryedale by-election when the Liberal-SDP Alliance overturned a Tory majority of more than 16,000.

However a key indicator this time may be whether they manage to take second place from Labour as they did on May 6 at nearby Richmond.

Parties and pundits will be watching for signs of defections by left-wing Lib Dem supporters in protest over the coalition with the Tories.

Any such switches might go to Labour or to John Clark, a Ryedale councillor, who is fighting for the separate Liberal Party. Its members decided not to join the Lib Dems in 1988 when the SDP and Liberals merged.

The huge rural constituency, stretching from outside Harrogate in the west to the North Sea, covers part of the North York Moors and then follows the Yorkshire Wolds east to the coastal town of Filey.

Author James Herriot lived and practised as a vet in Thirsk.

The constituency has a high rate of owner-occupiers and low unemployment. The economy is largely based on tourism and agriculture, though many residents commute into York.

In addition to the market towns of Thirsk and Malton, other population centres include Kirkbymoorside, Pickering and Helmsley, close to the impressive gothic ruins of Rievaulx Abbey.

Calculations for the Press Association, BBC, ITN and Sky News by Plymouth University experts Professors Colin Rallings and Michael Thrasher suggest that if the boundary alterations had been in force in 2005 Conservatives would have had a 14,117 majority.

The notional line-up is: C 25,702; Lab 11,585; Lib Dem 9,314; Ukip 1,522, Others 1,417.

The May 27 candidates are: John Clark (Liberal Party), Toby Horton (Ukip), Howard Keal (Lib Dem), Anne McIntosh (C), Jonathan Roberts (Lab).

The election was postponed after the death of a Ukip candidate.