Women should be able to obtain emergency contraception in advance of having unprotected sex, a sexual health charity has said.
The morning after pill can be taken up to 72 hours after sex
The Family Planning Association (FPA) says the morning after pill is more effective the sooner it is taken.
Having the pill to hand would mean women would not have to spend time finding a doctor or clinic to prescribe it, says the FPA.
Some family planning clinics do already give out the pill in advance.
The morning after pill can be taken up to 72 hours after unprotected sex has taken place.
The FPA said women were more likely to use emergency contraception if they had it in advance, and did not have to see a doctor to obtain a prescription.
The association said studies had shown advance prescribing was safe and effective - and that it did not mean women had more unprotected sex, or that they used the morning after pill as a regular form of contraception.
The FPA said over 75% of women surveyed would like to have emergency pills in advance.
But over 80% did not know they could ask for the service.
Fourteen per cent of family planning clinics said they already offered advance prescriptions of the morning after pill to women.
And over 40% said they would do so if asked.
Many clinics said they did not give out advance prescriptions more widely because of concerns over cost.
The FPA, which surveyed 100 women and 100 family planning clinics, called for advance prescriptions of the morning after pill should be more widely available.
Anne Weyman, chief executive of the FPA, said: "Emergency pills are more effective the sooner they are taken after unprotected sex.
"Women may not always be able to get to a GP or clinic quickly, especially at weekends, so having these pills to hand can offer the best way to prevent an unplanned pregnancy."
She added: "This 'access through the bathroom cabinet' is ideal for women whose method 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."
But Paul Danon of the Society for the Protection of the Unborn Child said: "The trouble is that the morning after pill doesn't always prevent a pregnancy - quite often it terminates it.
"This is just another reason for us to say the prescribing of it, and the availability of it, just has to stop."