The new calls have been prompted by research showing that the pill should be taken as soon as possible after unprotected sex to maximise the chances of preventing pregnancy.

Campaigners want pill available at pharmacies

Emergency contraception pills are currently licenced for use up to 72 hours after sex.

World Health Organisation researchers found that the pregnancy rate was 2% if the pill was taken within 47 hours of sex.

But if the pill was taken between 49 and 72 hours after sex, the pregnancy rate rose to 4.7 per cent.

WHO researchers also found that a progesterone-only version of the pill was more effective than the combination pill - the only version currently available in the UK. It also had fewer side effects, such as nausea.

Ann Furedi, director of Birth Control Trust said: "This new evidence strengthens the case for making Emergency Contraception available from pharmacies.

"There is also clearly a case for encouraging doctors to prescribe emergency contraception for women to keep at home in case they may need to use it."

'Too much hassle'

At present, the UK version of the pill, marketed as Schering PC4, is only available on prescription.

Ms Furedi said: "Throughout Britain there are just under 200,000 abortions every year. A significant proportion of those could be prevented if these women used emergency contraception.

"One of the reasons why they don't use it is because they cannot get hold of it very easily. If they can't get an appointment to see their doctor, sometimes it is just too much hassle, so they decide to take a chance on becoming pregnant."

Emergency contraception pills are essentially high doses of traditional birth control pills, which disrupt a woman's hormonal pattern to prevent pregnancy.

However, some, such as RU 486, cause the abortion of a fertilised egg that has already implanted in the uterus wall.

Dr Adrian Rogers, director of the Conservative Family Institute, said using the emergency contraception pill was morally wrong.