Unions and women’s pressure groups stepped up demands for compulsory pay audits after the pay gap between men and women widened again.

The annual survey of pay by the Office for National Statistics found that after years of a slow and gradual erosion of the pay gap, the difference increased for the year ending in April.

Pay gaps differ substantially between the private sector and the public sector, where unions have waged many high-profile equal pay claims. In the private sector the pay gap is 21.7 per cent while in the public sector it is 13.8 per cent.

The Office for National Statistics said that the gap had been partly widened by an increase in women going into full-time work – an increase of 96,000 or 1.4 per cent compared with an increase of 17,000 or 0.2 per cent for men. The ONS could not say why more women had gone into full-time work. Women make up 39 per cent of the full-time workforce.

The gap in the median hourly rate for full-time workers widened from 12.5 per cent to 12.8 per cent. The gap for the mean, or average, hourly rate rose from 17 per cent to 17.1 per cent.

Katherine Rake, director of the Fawcett Society, which campaigns for women’s equality, said: “In a time of economic difficulty, women have today received particularly dire news. After years of painfully slow progress in closing the pay gap, we have now actually gone into reverse gear with the pay gap widening over 2008 for women working full and part time. This sadly demonstrates that the Government has failed to take serious action to combat discrimination still facing women in the labour market.”

So far the Government has backed away from compulsory pay audits for all employers, preferring a voluntary approach. But the Fawcett Society said that only 17 per cent of British companies had volunteered an audit.

Brendan Barber, TUC General Secretary, said: “This is an injustice for both women and men. As redundancies mount, more women may find themselves as the sole or main income earner. It is more important than ever that they are not underpaid.”

Mr Barber added: “The link between fair pay and checking pay systems is clear. The case for mandatory pay audits is stronger than ever.”

Kamaljeet Jandu, inclusion and equality officer at the GMB, said: “It is very disappointing that the gender pay gap has widened when there is an expectation that progress will be made in narrowing it. Male workers at the top of the tree account for a lot of this gender pay gap. GMB has been promised that equal pay audits will be part of the Government’s procurement policy.”

The pay survey, which was drawn from tax returns of 146,000 people, also found big differences between overtime pay and bonus and commission pay for men and women. Mean overtime pay for men was £28 per week compared with £10 for women and pay made up of commissions, bonuses and/or incentives was £13 per week for men and £5 for women.

The survey found that the gross median weekly pay for men rose in the year to April by 4.6 per cent for men to £521 – an annual rate of £27,500 – and by 4.4 per cent for women to £412 – an annual rate of £21,400.

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