Brown slumps in latest opinion poll

LONDON (Reuters) - Prime Minister Gordon Brown slipped further behind the Conservatives in an opinion poll published on Saturday that contradicted the findings of a rival survey published earlier this week.

The ICM poll in the Guardian newspaper suggested voters have doubts about Brown's tax cutting and borrowing plans to ease the pain of the economic downturn.

It said the Conservatives had extended their lead over Brown's Labour government to 15 points, enough to ensure a substantial parliamentary majority if repeated at an election -- not due till 2010.

Some 45 percent of those surveyed backed the Conservatives, up three points and matching a peak of support achieved twice over the summer in ICM polls, compared to just 30 percent for Labour.

The findings were in sharp contrast with a YouGov poll published on Wednesday which said Brown had actually narrowed the Tory lead to just four points, his best performance in many months.

Both surveys were conducted after the government announced plans on Monday for a 20 billion pound ($30.86 billion) stimulus package to support the flagging economy that include a temporary cut in Value Added Tax to 15 percent and new 45 percent tax band for higher earners.

The opposing findings of the polls may be due to their differing methodologies. ICM, which conducted its latest poll on November 26 and 26, contacts voters by telephone. YouGov uses email to reach a panel of respondents.

(Reporting by Tim Castle; Editing by Jon Boyle)