Video: where have all the Labour voters gone?

David Cameron is preparing to avenge an historic by-election defeat after the Liberal Democrat MP Mark Oaten confirmed that he was considering leaving Parliament before the next general election.

Mr Oaten, 44, told The Times yesterday that he was talking to potential employers and could leave his Winchester constituency before the expected poll in 2010. His departure would hand the Tory leader the chance to maintain momentum and an opportunity to destabilise Nick Clegg, his Liberal Democrat counterpart.

Conservative officials said that they were relishing the chance to win back the constituency.

At the 1997 general election Mr Oaten took Winchester from the Conservatives by a margin of just 2 — and then crushed their candidate, Gerry Malone, by a margin of 21,556 in a by-election after they had successfully challenged the result in the courts. He rose to become the Lib Dem home affairs spokesman and announced a leadership challenge after Charles Kennedy resigned in January 2006. Shortly afterwards he left frontline politics, confirming that he had paid male prostitutes for sex.

Contacted yesterday over rumours that he was preparing to depart, Mr Oaten confirmed that he had had meetings in America with a potential employer and said that he had been honest with his colleagues about the possibility that he might leave before the general election.

“There are lots of conversations going on, some involving stuff abroad, some on stuff in this country. I hope that I can leave at the general election but I have been frank about the fact that it might be before that,” he said.

Mr Oaten insisted that he had not, as yet, secured another job. “There’s no offer on the table that I’m chewing my leg off about,” he said.

He was also nearing the completion of an autobiographical book that would deal candidly about the circumstances of his downfall. “It’s about how not to turn 40,” he said.

After the Tories’ big by-election victory at Crewe & Nantwich this month, the party is bullish about overturning the Lib Dems’ Winchester majority of 7,476. “It would be a big test of how effective David Cameron can be in attracting Liberal Democrat voters but it’s fair to say we would relish the chance,” a Tory source said.

The seat is to be redrawn at the next general election but a by-election would be fought on the existing boundaries. It is thought that Steve Brine, already selected as a parliamentary candidate, would fight it for the Tories.

A spokeswoman for Mr Clegg declined to comment on what will be viewed by many Lib Dem MPs as a betrayal of the party. However, senior Lib Dem sources said that Mr Oaten confirmed that he had told Mr Clegg that he was considering leaving Parliament early and that the party was confident of holding the seat.

The immediate task facing Mr Cameron is to hold Henley, the seat being vacated by Boris Johnson, the newly elected Mayor of London. About a thousand local Conservatives are expected to vote today to select a candidate from a shortlist of three.

John Walsh, the party’s agent in Henley, said that it had pencilled in June 26 as a date for a contest. It will serve a writ in the Commons next week, after the recess. If the by-election cannot be held next month, Mr Walsh said, the next likely date was October. There had been speculation of a July 3 date, but Mr Walsh said that would be logistically difficult as it would coincide with the Henley Regatta.

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