The new legal opinion challenges the basis of Mr Patten's draft guidelines, issued in December, and will inflame a controversy in Whitehall over the part that should be played by teachers in reducing teenage pregnancies and the risk of Aids.
The opinion, which is being studied by both the Health and Education departments, rejects a declaration by the Department for Education that giving contraceptive advice to girls under 16 - the age of sexual consent - could amount to a criminal offence.
Although both departments have played down any suggestion of a dispute, the Department of Health is known to have been pressing the Department for Education to take a less restrictive and more pragmatic view of sex education than Mr Patten's guidelines suggest.
The opinion, prepared for the National Children's Bureau by Alan Levy QC, is likely to be seized upon by officials at the Department of Health who have been arguing that Mr Patten's guidelines could militate against the Department's target of reducing teenage pregnancies by half before 2000.
The controversy over sex education goes to the heart of the dilemma faced by the Government over its 'back to basics' message. On the one hand the policy was launched by John Major at the party conference last October after a series of speeches highlighting the problems caused by single parenthood; on the other, its appeal to the Tory 'moral majority' has if anything increased hostility to explicit sex education which many experts believe would sharply reduce teenage pregnancies.
Mr Patten's guidelines say sex education 'must be provided in such a manner as to encourage young people to have regard to moral considerations and the value of family life'. They also reaffirm the right - enshrined by a government amendment in the 1992 Education Act - for parents to withdraw children from sex education.
Mr Levy's opinion also casts doubt on that right, suggesting that while it would be a matter for the courts, pupils might be able to bring an action under the 1989 Children Act challenging a parental instruction not to attend.
Although not referred to in Mr Levy's opinion the Sex Education Forum - an umbrella body pressing for expansion of sex education is schools - has cast doubt over whether the Act conforms with a 1976 European Court finding against a group of Danish parents who withdrew their children from sex education classes.
The forum argues in its draft response to Mr Patten's guidelines that there is a 'large body of authoritative research' showing that sex education does not increase sexual activity among young people 'but rather may delay the onset of sexual activity and increase the adoption of protected sex among those already active'. On the provision of information on obtaining contraceptive advice, Mr Levy's opinion cites the Victoria Gillick case in 1986 in which the House of Lords held that it was unlikely that a doctor giving an under-age girl contraceptive advice, without parental consent, but believing he was acting in the girl's best interests, would be committing an offence.
Mr Levy says that while the relationship between pupil and teacher is different from that between doctor and patient, he believes the courts would be likely to take the same view in the case of teachers.
The most recent research shows that nearly 19 per cent of young people report having had sexual intercourse before the age of 16. But the under-age group is also the least likely to use contraception, with 50 per cent not doing so.
The issue surfaced in a Cabinet paper leaked last year which pointed out that the rate of conception among 15- to 19-year-olds in England and Wales is one of the highest in Europe, with 8,000 girls under 16 becoming pregnant each year.
That is seven times the corresponding rate in the Netherlands, which has more sex education in schools and where low-cost contraception and abortion are both more freely available.Reuse content