The policy has split the Labour Party, but also divides its opponents. The Conservatives have attacked it as "political correctness run wild", but are also embarrassed by Labour's choice of 39 women candidates in winnable seats. Only two women have been chosen to fight safe Tory seats, while three Tory women MPs are retiring. Senior sources at Tory Central Office say they will ensure that the approved list of candidates - at present split 450-150 in favour of men - is split half-and-half between the sexes after the next election, although local Tory associations would not be required either to shortlist or select women.
Meanwhile, Peter Jepson, a part-time law lecturer blocked as a Labour candidate for two London seats, sees himself in the role of David against an establishment Goliath - a view dismissed as "self-pitying" by Labour supporters of women's quotas, who point out that men will still comprise over three-quarters of Labour MPs after the next election.
Mr Jepson will represent both himself and Roger Dyas-Elliott, who is barred as a candidate in Keighley. He will have "limited" help from the Equal Opportunities Commission (EOC), and unpaid help from a newly qualified barrister. The Labour Party will be represented by a leading Queen's Counsel, James Goudie, who once shared an office with the Labour leader Tony Blair in the chambers of Lord Irvine, the shadow Lord Chancellor.
Mr Jepson, who says he is in favour of more "positive action" to help women into Parliament, claims the policy breaches the 1975 Sex Discrimination Act and the 1976 European equal-treatment directive. The case will turn first on whether, under the Act, the Labour Party in safe Labour seats can be seen as a professional body conferring qualifications by controlling access to the "profession" of being an MP. The tribunal is likely to take the view that the choice of MP is a matter for constituency voters, but if there is ambiguity in the Act, Mr Jepson claims it must be interpreted in line with the Euro-directive.
Mr Jepson,44, a PhD student, has a degree in labour law and is studying race discrimination for his thesis. He has been a party member for 16 years. He was a local councillor in Tameside, Greater Manchester, until 1989.
Labour's policy has split legal opinion. Last year the EOC obtained counsel's opinion from Michael Beloff QC - head of Mr Blair's wife Cherie Booth's legal chambers - that the policy was lawful. But Lord Lester, who advised the former Home Secretary Roy Jenkins on discrimination law, says it is not.
Mr Blair has been unenthusiastic about the policy. In July, he described it as "not ideal at all", and said it would apply only to the next general election, before coming under review.
The case, postponed from 27 July, is scheduled to continue until next Monday.
Leading article, page 14