The government's actions are making EU employment legislation "redundant", a Brussels commissioner has warned.

European Commission employment chief Anna Diamantopoulou told EUpolitix.com that if other European countries follow Britain's example and "abuse" an opt-out on working time rules then the employment rights legislation will become meaningless.

Her comments on the working time directive will attract attention around the continent as the UK bids to defend its right to opt outs at this weekend's summit on the new EU constitution.

Diamantopoulou said the opt-out was a necessary "tool" that gave countries flexibility but should only be used "as an exception not as a rule".

"Of course if everybody opts-out and at the same time abuses the opt-out then there is no directive and it is totally empty," she said.

Britain is the only EU country currently exercising its right to opt-out on the enforcement of a maximum 48 hour week.

Other union members fear that the move gives the UK an unfair competitive edge and could lead to copycat actions.

"First of all, the abuse of the opt-out has a very worrying impact on workers, second, it destroys the level playing field of companies at a European level, and third it undermines the whole concept of what we call 'working time' in economic and social terms," the commissioner added.

"I believe the opt-out could be a tool and we must use it when there is a need.

"It is something that adds to the need for flexibility in the labour market but it must be under concrete rules and only used as an exception, not as a rule."

Unions have called for Brussels to apply more pressure on ministers to apply the law.

"It's about time the European Union made sure that its working time rules made a difference in the UK," TUC general secretary Brendan Barber said.