A third of working mothers are leaving full-time jobs for part-time positions or giving up altogether, according to BBC findings.

The study, commissioned by Panorama, deals a blow to government initiatives to encourage mothers back into the workforce.

The research has also established strong links between children whose mothers are not around during infancy and poorer exam results later in life.

University of Bristol researchers analysed the working patterns of 560 mothers who returned to employment after the birth of their first child.

The survey showed that within two years of giving birth, more than one third had given up their full-time jobs, with 17% switching to part-time work and 19% giving up altogether.

One mother, Cathy Schofield, gave up a successful publishing career to spend more time with her son.

'Guilt-ridden'

She tells Panorama: "I didn't think I would find myself not exactly being hounded out of work but having my working day made so guilt-ridden that I just couldn't bear to carry on."

Professor Heather Joshi carried out separate research for the Institute of Education which linked mothers' working patterns to child educational achievements.

"There may be something in the child's early development that equips them better to face these undoubted challenges of doing public exams," she said.

"GCSEs, A-levels and degrees require a lot of skills, personality and motivation.

"It's a big challenge. Maybe having a mother at home when they were under five equips them better."

The programme's findings back critics of government plans to encourage women back to work by offering tax credits.

They want legislation allowing women to demand their jobs back on a part-time basis, but there are fears that this could make women a less employable option in the eyes of company bosses.