The Trades Union Congress (TUC) general secretary Brendan Barber has dubbed an increase in working hours as "disturbing".

According to the TUC, more than one in eight work more than 48 hours each week, with as many as one in six Londoners putting in 48 hours plus.

The TUC says the findings point to a lack of enforcement of the rules that protect workers against an average working week of no more than 48 hours, unless they opt out of the working time rules.

The latest Labour Force Survey shows that 93,000 more people now work more than 48 hours a week, taking the total to almost three and a quarter million. This is a rise to 13.1% from 12.8% last year.

The biggest rises are in the south east, with an increase of 28,000 to 525,000, and London an increase of 25,000 to 481,000.

In Wales it rose by 1.3%, to 12.2%.

Barber said: "These are very disturbing numbers. No-one should forget that 48 hours is six eight-hour days - more than enough for anyone every week. There is undoubted abuse of the law, but employers know they can get away with it because it is rarely enforced."

He added: "Neither the Health and Safety Executive nor local authorities who share responsibility for enforcement have the resources to implement the law. And the government knows that employers can abuse the opt-out as ministers consulted on ways to close loopholes in 2004, but have yet to bring forward any concrete proposals for change. The current discussions on how best to protect vulnerable workers and enforce existing rights must include working time rights and closing the loopholes that make a voluntary opt-out a joke."

According to the TUC, the opt-out clause is widely abused with two-thirds not even asked to opt out before they are expected to work in excess of the 48 hours and a quarter of those who signed up not given any real choice about opting out.