They seized the formerly safe Labour seat by a margin of almost 8,000 votes, overturning the 7,000 majority achieved by the late Gwyneth Dunwoody in 2005.

It is another blow for the PM after Labour's drubbing at the May 1 local elections - and a first by-election win for the Tories since 1983.

Tory winner Edward Timpson admitted the by-election was probably the first time many of his voters had backed the Conservatives.

"I have a message for you," he said, after the result was announced. "I am on your side and I won't let you down."

Mr Timpson added: "I am going to stand up for local families, local jobs and, whenever I need to, stand up to the Government on your behalf."

Defeated Labour candidate Tamsin Dunwoody shrugged off criticism of her tactics in the by-election campaign. Referring to attempts to depict Mr Timpson as a Tory toff, she called the campaign "robust but fun".

She also warned Mr Timpson: "It is an honour to serve the people of Crewe and Nantwich - an honour I hope you take seriously. I will be watching you."

David Cameron would cruise into Downing Street with a Commons majority of more than 300 if the Crewe and Nantwich swing was repeated across the country at a General Election.

Result in full: Edward Timpson (C) 20,539; Tamsin Dunwoody (Lab) 12,679; Elizabeth Shenton (LD) 6,040; Mike Nattrass (UKIP) 922; Robert Smith (Green) 359; David Roberts (Eng Dem) 275; The Flying Brick (Loony) 236; Mark Walklate (ND) 217; Paul Thorogood (CTDP) 118; Gemma Garrett (ND) 113.