Gill Lumsden, the new chairman of the Incorporated Association of Preparatory Schools, was expected to urge members meeting in Dublin this week to refuse to give their key stage 2 results to the paper.

She said she proposed to sabotage the Sunday Times’ league table of preparatory schools because not all preparatory schools are given the chance to send in their results.

Mrs Lumsden, headteacher of Kensington prep school, London, is the second women to become chair of the association in more than a hundred years, and the first mother to hold the post.

She will use her year in office to persuade more women to become heads. Only 27 per cent of heads in the association are women.

Mrs Lumsden, a head for 15 years, said: “An awful lot of women don’t go for headships as they still consider it to be a man’s world.”

She also said that independent schools could be affected by the Government’s review of charities, warning that education may not be automatically accepted as a charitable activity.