Labour MEPs have defied Tony Blair by voting to impose shorter working hours on British businesses and public services.
They backed proposals in the Strasbourg Parliament to scrap Britain's opt-out from rules which ban anyone from working more than 48 hours a week.
The regulation, called the Working Time Directive, will apply to public bodies such as the NHS as well as industry.
Mr Blair had warned that Britain's exemption was essential for labour market flexibility.
But Labour MEPs ignored their party leader just as his authority was also being questioned at Westminster, following the General Election which saw Labour's majority cut.
West Midland Labour MEP Neena Gill insisted last night: "We are not members of the Government."
Gordon Brown, the Chancellor, has also warned that a maximum 48-hour working week would undermine productivity and Britain's ability to compete in the world.
Labour MEPs joined fellow Socialists in the European Parliament in voting against the opt-out.
It was won by John Major 12 years ago and has been a bone of contention in Europe ever since.
Workers already have the right to refuse to work more than 48 hours. But they are currently able to work longer if they sign an agreement with employers.
This will change if the vote in the European Parliament is upheld by EU ministers.
Ms Gill said: "We are Labour representatives in the European Parliament.
"What we do is to scrutinise European legislation for the benefit of the people of Britain.
"The Labour MEPs believe this is progressive legislation which will provide a good work-life balance for British workers."
But Conservative West Midland MEP Philip Bushill-Matthews said: "There could be no clearer sign of Tony Blair's waning authority than the decision of Labour MEPs to vote in favour of abolishing the opt-out.
"The only alternative view is that the government is in fact quite prepared to see the opt-out go, and has been happy to let Labour MEPs follow their own agenda while spinning a very different line from London to woo the business vote.
"Either way, the abolition of the opt-out will have a devastating effect on British business.
"It's also a serious blow to the two million workers who take advantage of the right to choose how long they work and how much they earn."
And West Midland Liberal Democrat MEP Liz Lynne said: "Labour MEPs today showed that despite the best efforts of Number 10, old Labour is alive and well, and voting down the UK government line from Strasbourg.
"They are blinded by ideology and can't see the dangers of removing workers right to opt-out.
"Of course there must be adequate provision against workers opting out under duress, but there are less drastic ways to achieve this. What is important is that wherever the opt-out is used it is truly voluntary, and reflects the best interests of workers."