An employment gap between mothers and fathers widens within three years of having children, even though only half of men initially earn more than their partner, research has shown.

Researchers at the universities of Bristol and Essex tracked the employment status of 2,281 new mothers over three years and 1,199 mothers over five years for the study, undertaken for the government equalities office.

About 90 per cent of new fathers were working full time or were self- employed three years after the birth of their child, compared with 27.8 per cent of mothers. More men also advanced their careers through promotion: 26 per cent of fathers were in a more senior role five years on from parenthood compared with 13 per cent of mothers.

The academics found that women with degrees were twice as likely to return to work full time as mothers with lower qualifications.

A large study found that men were the main or sole earners in 54 per cent of couples a year before they had children, with 31 per cent earning equal amounts and women the chief breadwinner in 14 per cent of households.

However, three years after having children, men were the sole or main breadwinners in 69 per cent of families and fathers and mothers earned similar amounts in only 20 per cent of couples.