Campaign groups and unions are urging the government and employers to quicken the pace of change.

It is hard to believe that women are still so consistently undervalued in the workplace

Julie Mellor, EOC chairwoman

"After 30 years of equal pay legislation it is hard to believe that women are still so consistently undervalued in the workplace," said Julie Mellor, chairwoman of the Equal Opportunities Commission.

The EOC believes companies should be forced to carry out pay audits unless they monitor their wage systems.

Also calling for reforms of equal pay and sex discrimination laws is the TUC, which is holding a London conference to celebrate the anniversary of the Equal Pay Act.

Women undervalued

"Women workers have put up with poor pay because of institutionalised discrimination and the fact that society has traditionally undervalued the kind of work they do," said general secretary John Monks.

The GMB general trade union plans to launch the latest in a series of equal pay claims against the NHS, on behalf of female hospital catering workers from Barnsley.

Female workers earn at least �65 a week less than men doing work of the same skill level, the union argues.

National officer Sharon Holder said: "Nothing has changed. These women are being treated as the Cinderellas of the health service."