A survey of companies found that one in five employees who had opted out of European working time regulations introduced last October felt they had been obliged to do so.

John Monks: 'No surprise'

The working time directive was set up to regulate the hours employees should put in each week, as well as holiday entitlement and rest breaks.

The legislation allowed for an opt-out, where UK workers could sign a voluntary waiver to the directive if they wanted to work more than the 48 hours a week stipulated.

However, the Today programme survey, conducted by Gallup, found that 14% of the people who had opted-out felt they had to sign the waiver.

A further six per cent felt they ought to.

The researchers had interviewed 6,000 workers, of whom 635 had opted out of the working time regulations.

The survey comes as the government prepares to make changes to the working time directive which would allow more opt-outs.

TUC general secretray John Monk said the survey confirmed what the unions had been hearing from many workers.

Adair Turner: 'Right to work longer'

He told the BBC: "It doesn't surprise me at all to hear the results of the survey.

"We get lot of information through the unions and from Citizens Advice Bureaux about workers who complain they are being pressurised, either by their employers directly or just by the culture of a particular workplace.

"Some are being threatened, and some are responding to the macho mood of 'I shouldn't go home early' and so on, which pervades many British workplaces."

The Confederation of British Industry said the survey showed that only 2% of the workforce felt under pressure to opt out, and that, of those who had opted out, 80% were happy to do so.

Adair Turner, director general of the CBI, said: "No-one wants unnecessary amounts of hours being worked, but ultimately individuals, and particularly the sort of people covered by the opt outs, can make their own decisions."