Equalities Minister Harriet Harman has been accused of exaggerating the pay gap between men and women.
Miss Harman has used the figure to justify unpopular measures contained in her Equality Bill.
But according to Sir Michael Scholar, the head of the UK Statistics Authority (UKSA), Miss Harman has put the size of the divide at almost double the real figure.
Sir Michael thinks that while ministers have claimed women are paid 23 per cent less than men, the true figure is more like 12.8 per cent.
He said the Equalities Office had appeared to ignore warnings from the UKSA that including part-time incomes in their calculations could be misleading.
The discrepancy has been pointed out amid warnings from businesses about the cost burden they are likely to face if the Equality Bill becomes law.
Yesterday the Association of Convenience Stores said it feared the Equality Bill “will just heap more costs and bureaucracy on small stores”.
Earlier this week MPs scrutinising the Bill at Committee Stage were warned of the damaging implications it could have for religious organisations in evidence from the Roman Catholic Church and the Church of England.
Under the current law, religious groups can restrict posts to Christians whose private conduct is consistent with the Bible’s teaching on sexual ethics. These posts must be for the purposes of organised religion, which could include jobs like a youth worker.
But under the Equality Bill the Government is specifying that this protection can only apply to posts that mainly involve leading worship or explaining doctrine.
The Bill’s explanatory notes make it clear that this protection “would not apply to a requirement that a church youth worker or accountant be heterosexual”.
In its evidence to MPs the Roman Catholic Church said that under proposed ‘harassment’ provisions the Bill could add to employment law, a church could be sued by an atheist cleaner who took exception to crosses and other religious displays in its buildings.
The Bill also introduces a new Equality Duty, which would force public bodies such as schools and the police to promote ‘equality’ on grounds including sexual orientation and transsexualism.
One campaigner has claimed this would see ‘gay rights’ entrenched in all aspects of public life.
There would also be a duty for public bodies to promote religious equality, but examples of extreme sensitivity to other religions in the public sector has raised fears that the new measures will simply marginalise Christians further.