The gap between the pay of women and men is wider than previously thought and has not narrowed as quickly as previous figures suggested.

Pay analysts Incomes Data Services said the difference between average hourly earnings of full-time male and female workers was 19.5 per cent last year, not the 18 per cent previously quoted.

Their report, which followed changes to the way annual earnings were calculated, said the gap has not closed as quickly over the six years to 2003 as earlier data had shown, narrowing by 1.7 per cent rather than two per cent.

It has prompted union leaders to step up their demand for firms to hold mandatory pay audits to make sure female workers were not earning less than their male counterparts.