Britain was hit yesterday by what trade unions have called the biggest wave of work stoppages since the Labour government came to power 10 years ago, with up to 400,000 public sector employees going on strike.

It was yet another blow to Prime Minister Gordon Brown just one day after he was forced by party rebels into a humiliating policy reverse over tax cuts.

Refinery workers at the Grangemouth oil refinery in Scotland are also set to strike in a dispute over pensions that could cause major fuel distribution problems.

Up to 200,000 teachers are staging their first national strike in 20 years in a bitter pay dispute with the government. Up to one third of schools in England and Wales are set to be disrupted.

?After three years of below-inflation pay increases, the prospect for a further three years of the same is the last straw,? said teachers? union leader Christine Blower.

Brown, whose popularity has plummeted in a string of crises and is battling to keep the economy on course amid global turmoil, has called the strike ?very regrettable? and urged teachers to reconsider their action.

But unions are in militant mood, determined to take on a government trying to keep a lid on public sector spending.

Millions of workers paid by the government have expressed disappointment and frustration over their latest pay deals as the cost of living has risen.

Yesterday, the teachers were joined in a coordinated wave of strikes by civil servants ? ranging from coastguards to driving test examiners. About 100,000 workers from 10 government departments are angry over pay rises capped below inflation, their union said. Their union leader, Mark Serwotka, said ministers only had themselves to blame.

Brown, who replaced Tony Blair as prime minister last June after 10 years as finance minister, has seen his ratings slide as the effects of the global credit crunch dent his reputation for sound economic management.

He could face a ballot box drubbing on May 1 in local elections, his first electoral test since he took over from Blair.