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LONDON - British Prime Minister Tony Blair's authority has again been challenged after another party revolt over flagship school reform plans.

The schools bill was passed by a huge majority of 324 in parliament at its crucial third reading thanks to support from the main opposition Conservative Party.

But 46 Labour lawmakers voted against the legislation, Labour's biggest revolt at this stage of a bill since the party first came to government in 1924.

Blair's standing within Labour has taken a battering in past weeks following dire local election results and relentless headlines of sleaze, scandal and government incompetence - and analysts said his authority was on the line.

"He's now in a situation where I don't think he would be able to get through any controversial piece of legislation without requiring support from the opposition," Philip Cowley, political analyst at Nottingham University told Sky television.

The vote came after an opinion poll by the Guardian newspaper and ICM put support for the opposition Conservatives - resurgent under new leader David Cameron - at 38 per cent, four points ahead of Labour.

Blair's authority has been on the wane since he said he would not seek a fourth term, while anger over the Iraq war and disillusionment after nine years in office has eroded his popularity with the public.

Blair has brushed off criticism of his public service reforms and calls to stand down. His office argues that the vast majority of Labour lawmakers back the reforms.

In a vote on amendments to the schools bill on Tuesday, local time, 69 Labour lawmakers rebelled, the biggest revolt since Blair won a third term last year.

In a previous vote on the same bill in March, 52 Labour lawmakers rebelled. Labour has a working majority of about 71 seats in parliament's lower house.

Opponents of the education bill argue that granting schools more freedom by giving them "trust" status will lead to a two-tier system that will exclude disadvantaged children from the best schools.