Britain's opposition Conservatives will likely fail to win power outright in the country's national election this spring, a poll of 100 key districts indicated Tuesday.

The Populus survey, published by The Times newspaper, questioned voters in districts where the Conservatives are seeking to oust incumbent Labour lawmakers.

David Cameron's Conservatives need to capture around 135 extra seats in the House of Commons from Labour and other parties to win a majority and form Britain's next government.

Prime Minister Gordon Brown has yet to announce the date of the election. It must be held by June 3, and is expected to take place May 6.

Labour now holds 346 of the House of Common's 646 seats - 57 more seats than all the other parties combined. The Conservatives have 193 seats, and the Liberal Democrats, 63.

Though Cameron's party has led in opinion polls for more than two years, current surveys suggest that neither the Conservatives or Brown's governing Labour party will win a majority.

The Populus poll questioned 1,500 people in the 50th to 150th Conservative target seats. It didn't conduct research in the first 50 targets, which the Conservatives are expected to win easily.

Labour had 38.2 percent support in those 100 districts and the Conservatives had 37.6 percent. The newspaper calculated those figures mean the Conservatives would be Britain's largest party overall, but wouldn't hold a clear majority.

It means Cameron would need to try to form a coalition with another party, or attempt to hold power as a minority government.

Britain hasn't had a hung Parliament after an election since 1974.

Cameron's prospects have been jolted in recent weeks by a furor over the vice chairman of the Conservative Party - and a major donor - Michael Ashcroft.

Ashcroft, a multimillionaire who holds dual British and Belize citizenship, has acknowledged that he doesn't pay U.K. taxes on foreign earnings.

The poll's margin of error was plus or minus 2.5 percentage points.