The British Pregnancy Advisory Service (BPAS) is handing out free supplies of the morning-after pill to women who want to keep emergency contraception at home in case of future need.
Emergency contraception aims to stop ovulation or fertilisation of an egg, or prevent a fertilised egg from implanting in the womb.
Chemists are allowed to provide emergency contraception to women before they need it, although some refuse to do so and few advertise the service.
As a result, many women do not realise they can keep a morning-after pill at home in case they have unprotected sex in the future.
In addition, pharmacies, family planning clinics and GP surgeries will close over the festive period, leaving women at risk of unplanned pregnancies as the morning-after pill is 90 per cent more effective if taken within 12 hours of unprotected sex.
Ann Furedi, chief executive of the BPAS, pointed out that sex is not always planned or prepared for.
"It's easy to get carried away, which is why we advise women to back up their birth control by keeping the morning-after pill at home," she explained.
"You don't wait until you get a headache to buy your pain relief - why wait until you've risked pregnancy to get the morning-after pill?"
The service will be available from BPAS clinics in Birmingham, Bournemouth, Brighton, Cardiff, Coventry, Leeds, London, Luton, Peterborough and Swindon from December 1st.
Independent advice on private healthcare