The Government was drawn into another row over its use of statistics today after the Labour deputy leader Harriet Harman was criticised by an official watchdog.
Sir Michael Scholar, head of the UK Statistics Authority, said Ms Harman's use of figures on the pay gap between men and women was potentially misleading.
His rebuke came after Ms Harman, also Minister for Women, used a figure for the gender pay divide more than twice the level used by official statisticians.
A press release issued by the Government Equalities Office on April 27 said women were on average paid 23% less per hour than men.
But the Office for National Statistics puts the figure more than ten points lower at 12.8%.
In a letter to Ms Harman, Sir Michael said the use of different figures was "likely to confuse the general public".
He added: "The Statistics Authority is concerned that this may undermine public trust in official statistics."
"It is the Statistics Authority's view that the use of the 23% on its own, without qualification, risks giving a misleading quantification of the gender pay gap."
A source said Ms Harman's department was warned about using the figure beforehand but went ahead anyway.
Both figures were taken from the same annual survey of hours and pay, and are based on average hourly earnings excluding overtime.
The ONS measure is based on full-time earnings alone while the GEO figure includes full-time and part-time workers.
Both men and women who work part-time are paid less, but the vast majority of part-time workers are women. That means including all part-time workers in the figure could exaggerate the pay divide.
Sir Michael said neither measure was "entirely satisfactory" on its own and suggested different ways to discuss the gender pay gap that were "impartial and objective".