Women should be able to receive advance supplies of the "morning-after pill", according to charities and the Royal College of Nursing (RCN).

The Family Planning Association (FPA) is calling for prescribing rules to be changed so that people can stockpile emergency contraception pills in their bathroom cabinet.

Women can now buy the morning-after pill over the counter at pharmacies but strict rules to chemists mean that they must ask customers whether they have had unprotected sex within the past 72 hours before they hand over the drug.

The FPA, the RCN and the British Pregnancy Advisory Service (BPAS) said the strict rules can make it difficult for women to get the morning-after pill on time. It must be taken within 72 hours of having unprotected sex and is much more effective when taken within the shortest possible time after intercourse. If taken within 12 hours, it is about 98 per cent effective, falling to 60 per cent if it is left until 72 hours after sex.

Anne Weyman, the chief executive of the FPA, said "Women may not always be able to get to a GP, clinic or pharmacist quickly, especially at weekends, so having these pills to hand can offer the best way to prevent an unplanned pregnancy.

"This 'access through the bathroom cabinet' is ideal for women whose method of contraception could fail or who cannot get to a health professional easily.

"Emergency contraception is a cost-effective prevention measure, and wider access for women would help prevent the financial and social consequences of unplanned pregnancy."

The FPA wants to see nurses being able to hand out the morning-after pill in advance to women visiting their GP or health clinic.

The calls have been welcomed by the RCN. Dr Beverly Malone, its general secretary, said: "We would support the idea of advanced provision. This would allow women the option of early use, especially at weekends or in the event of failed contraception."

Contrary to popular opinion, most women who have to deal with an unwanted pregnancy were using some form of contraception. Nearly half of women who have an unwanted pregnancy say that they were using the contraceptive pill at the time but it either failed or they did not take it properly. A further third of unwanted pregnancies happened even though the couples were using a condom.

The Government changed the prescribing rules for the morning-after pill last year from prescription-only to making it available over the counter, in a bid to cut soaring rates of teenage pregnancies.

It has meant that girls and women can buy the pills at chemist counters but there are still problems. A woman told last month how a pharmacist had refused to sell her the emergency contraception because he had strong religious beliefs.

Ann Furedi, the chief executive of the BPAS charity, said: "Unfortunately, the current system for buying emergency contraception creates a blame culture, interfering with women controlling their own fertility, as they have to, in effect, justify why they want to take the pill."

But the calls for yet more relaxed prescribing of emergency contraception pills will infuriate anti-abortion campaigners, who believe that the move encourages promiscuity and unsafe sex.