June 12 (Bloomberg) -- David Davis, the lawmaker in charge of home affairs policy for Britain's opposition Conservative Party, resigned his seat in Parliament to force an electoral contest over government limits on civil liberties.

Davis, 59, will campaign to return to the House of Commons, arguing against Prime Minister Gordon Brown's national identification card program and his plan to let police detain terrorism suspects up to 42 days without charge.

``This is a by-election against the slow strangulation of fundamental British freedoms by this government,'' Davis told journalists today in London.

The decision undermined efforts by David Cameron to unite the Conservatives against the Labour government since his victory over Davis in a contest to lead the party in 2005. Davis, who favored stronger resistance to Brown's anti-terrorism package, told Cameron about his decision last night.

``This is a distraction that takes the focus of senior Conservatives away from fighting Gordon Brown,'' said Andrew Cooper, chief executive of Populus Ltd., which conducts opinion polls for the Times newspaper. Voters may ``regard it as an annoyance, a selfish thing to do.''

Nationwide, the Conservatives led Labour by 20 percentage points in a Populus poll this week. The Conservative share of the vote in Davis's constituency rose 4.2 percent in 2005.

`Risky Strategy'

``It is a little bit of a risky strategy,'' Mark Shephard, a lecturer in politics at the University of Strathclyde, said in an interview. ``It will be another chance for the people to give the government a bloody nose, but if there is an internal split in the Conservative Party, then that is a worry for Cameron.''

Labour lawmakers ridiculed the move as a political stunt. The Liberal Democrats, whose candidate came in second in Davis's constituency of Haltemprice and Howden in northern England two years ago, said they would not contest the by-election.

``Most people will see this as an irresponsible act,'' Tom Watson, a junior Cabinet Office minister, said in an interview. ``It is an unnecessary by-election costing the taxpayer tens of thousands of pounds.''

Davis has held the seat since 1987 and won it with 22,792 votes in 2005, a margin of 5,116 votes over the Liberal Democrats, who came in second. Labour's candidate placed third with 6,104 votes.

`Comic Opera'

``It's like something out of Italian comic opera,'' Labour lawmaker Denis MacShane said on BBC News 24. ``It's a huge blow to David Cameron. It just shows, two years away from a general election, how unfit the Conservatives are to run this country.''

Cameron called Davis's decision ``courageous.'' He learned about the plan last night, the same time Davis told the Liberal Democrat leader. Cameron picked Dominic Grieve to replace Davis as the Conservative lawmaker in charge of home affairs policy.

``I absolutely agree with him about the appalling decision to have 42-day detention without charge,'' Cameron told broadcasters while he was visiting Cornwall. ``I wish David Davis well. I know the Conservatives including me will wish to go support him.''

Yesterday, Brown's government relied on support from the Democratic Unionist Party to win a parliamentary vote on the 42- day detention plan, which was opposed by Liberal Democrats and the Conservative Party and by 36 Labour members of Parliament.

Ann Widdecombe, a Conservative lawmaker, broke with her party to vote for the government on the detention plan, an indication of unease among opposition lawmakers that Brown is taking a tougher line on that security issue than Cameron.

The House of Lords, the upper chamber of Parliament, must approve the plan before it can become law. Since no party has a majority in that house, Brown will have difficulty getting the 42-day provision through unscathed.

``The Liberal Democrats have consistently opposed this unnecessary and illiberal proposal which poses a threat so serious to British liberties that it transcends party politics,'' Liberal Democrat leader Nick Clegg said. ``We will not stand a candidate at the forthcoming by-election.''

To contact the reporters on this story: Kitty Donaldson in London at kdonaldson1@bloomberg.netMark Deen in London at markdeen@bloomberg.net

Last Updated: June 12, 2008 12:01 EDT