WHEN she began advising women on contraception on March 17, 1921, Marie Stopes was a trailblazer - for Britain was not a sexually-enlightened nation.

Ignorance was so rife that Stopes, who married in 1911, had been a wife for more than a year before she worked out that she was still a virgin and her husband was impotent. But this disastrous first marriage did have one positive outcome - Stopes became determined to save other women from the ''sexual humiliation'' she had suffered.

Not only did she open her clinic in Marlborough Road in Holloway, north London, she also wrote Britain's first sex manual, Married Love.

Stopes' quest, to educate the nation and make birth control more widely available, was a vital one.

At that time, more than 3,000 women a year were dying in the UK and thousands more were becoming ''chronic invalids'' as a result of pregnancy or giving birth.

The doctor was convinced that child survival rates, as well as women's health, could be greatly improved by birth spacing. She recommended a gap of two years between pregnancies to improve survival rates for infants and mothers - a policy which the World Health Organisation still recommends today.

Stopes also saw that contraception had to improve and dreamed of the day when a perfect form of birth control would be invented.

In 1923, she wrote prophetically in her book, Contraception: ''The absolutely ideal method of contraception has not yet been devised.

''It is perfectly possible to imagine some injection, serum, toxin or internal secretion, which might render the ovum or sperm respectively incapable of playing its part in fertilisation ... its existence, however, is purely theoretical.''

When Stopes penned this, the contraceptive pill was still decades away. It was not launched until 1960 - two years after her death.

In the 1920s, couples had to rely on basic methods. For men there were rubber condoms or penile pins or studs to ''close'' the penis.

Women's options included diaphragms, an early female condom and painful-sounding, wishbone-shaped studs to close the cervix.

Some couples resorted to still more basic methods like salt, lemon juice or vinegar douches. Others tried breast feeding or the even more dubious ''sitting upright the moment after ejaculation has taken place and coughing violently.''

Tony Kerridge, spokesperson for Marie Stopes International, says: ''We're still some way off the perfect contraceptive. There is no modern method which is 100 per cent effective."

Emeritus Professor David Baird, from the Centre for Reproductive Biology at the University of Edinburgh, says the 30 professional scientists and researchers at his unit are not necessarily looking for one universal, magic solution but here are some suggestions:

l A contraceptive patch, which will be stuck to the woman's body and will deliver a combination of oestrogen and progesterone, will be with us by 2002.

l Male pill. This may be available within the next five years, but will women trust men to take it?

l Bisexual bikinis. A Japanese company has developed a pair of latex underpants with a built-in condom facility, which could be used by men or women.

l Smart hormones which will only act on the reproductive system when you want them to. They should be available by 2010.

l Microbicides. Another long-term goal, compounds which work as a spermicide but can also stop people getting sexually-transmitted diseases, particularly HIV