Do you know why middle class working mothers are leaving jobs? Because they are unwilling to behave like men, a new research shows.

Mothers in professional and managerial jobs are expected to stay till late or get in early even if they have negotiated reduced working hours.

They have to socialise with colleagues or clients in the evenings - even though this clashes with their childcare responsibilities, said researchers from the University of Leicester in Britain, revealing the masculine culture of the workplace.

"They must do so because working culture is still organised by men, who are less involved in childcare. Many mothers respond by leaving their jobs," said Shireen Kanji, a senior lecturer at the University of Leicester's school of management.

"Unless mothers mimic successful men, they do not look the part for success in organisations," added lead author Emma Cahusac, a series producer of BBC Television's The Culture Show.

The researchers interviewed 26 mothers based in London who had quit their jobs while pregnant, or following their return to work, but before their first child reached school age.
Twenty one of them quit their jobs voluntarily - often because they had been sidelined after returning to the office.

Many of the interviewed women found it hard to combine work and motherhood because of the dominant culture of presenteeism - the notion that they should be at their desks until late even if there was nothing to do.

"I would be in work by eight but I would have to leave by six and actually I could do the job perfectly well," Susan, an ex-banker, told researchers.

Susan said her six o'clock departure provoked "barbed comments" from a woman who did not have children.

The researchers also found that before they had children themselves, women not only accepted but encouraged the masculine culture of the workplace.

The mothers interviewed also needed to hide the fact that they were parents - imitating a masculine trait.

The male partners never talked about their families. They have been very adept at keeping that separation between work and home, added Nadia, a lawyer.

Mothers had to hide the fact that they were taking time off to look after sick children.

"You definitely would have to say you were sick, not the kid was sick," said a mother who held a senior position at a charity.

"Many women leave high-powered jobs because they are relegated to lesser roles and feel the need to suppress their identities as mothers," Kanji said.

The findings were published in the journal Gender, Work and Organization.