Some people try accident and emergency departments. But overstretched hospitals are reluctant to provide emergency contraception, according to a recent report in the Journal of Accident and Emergency Medicine.
"We rang one hospital the other day," says Rachel Garbutt, from Manchester's Brook advisory clinic, "and they only had two pills left, when you need to take four."
"A&E isn't the place to go," agrees Toni Belfield, director of information at the Family Planning Association. "It really should be your own GP or family planning clinic."
Getting emergency contraception isn't really an "emergency", even though it may feel like one. The "morning-after pill" is, in fact, a misnomer. Many women believe they need to take it almost immediately, but the pills are effective within 48 hours and can still work up to three days after unprotected sex.
Getting a fast GP appointment is not always easy, and an added problem is surgery hours, which are notoriously inconvenient. "It may mean taking time off work or out of school," says Ann Furedi, director of communications with the British Pregnancy Advisory Service. "Faced with a major inconvenience, the temptation is to say it won't happen to me - I'll hope for the best."
Ease of access to emergency contraception is just one element in any government policy to tackle Britain's teenage pregnancy rates. Nationally, the rate is seven times higher than in the Netherlands.
In a pioneering and controversial move, Hayesfield Upper School in Bath has set up a clinic offering emergency contraception to girls during school hours, using a nearby GP. Although the school won recognition for the initiative from the Government's Social Exclusion Unit, it led to some adverse press coverage, and the school's governors decided to ban staff talking to journalists.
Alison Hadley, policy officer at the Brook Advisory Clinics, says: "It's a brilliant campaign. Tony Blair should be saying that this is fine and the government supports this."
Brook runs 18 advisory clinics around the country, with a free service for under 25s, open after school or at weekends. It is another option for emergency contraception.
"Sometimes girls come here, pregnant, who have not heard even heard of the morning after pill," says Ms Hadley. "Sometimes they have, but are under 16 and don't want to go to their GP, as they don't know whether it is confidential."
Family planning clinics are an option, although many only offer clinics for limited hours on certain days - hopeless if that doesn't fall within your 72-hour "window."
If you are prepared to pay, private clinics like Marie Stopes will provide emergency contraception for pounds 25 (pounds 20 for students). They are open weekdays and Saturday mornings.
One Boots store in Glasgow is offering drop-in contraceptive advice, including emergency contraception, at a twice-weekly clinic.
Many family planning experts believe that emergency contraceptive pills should be available over the counter at pharmacies; others feel GPs could prescribe them to patients in advance, just in case.
"Emergency contraception should not be seen as a permanent solution," says Ann Furedi of BPAS. "It is not as effective as planned contraception. But unprotected sex happens - and that is a fact of life."
For more information, call Brook information line on 0171-713 9000
What is it? Four tablets, a combination of oestrogen and progesterone, taken within 72 hours of unprotected sex. The second two are taken 12 hours after the first two.
Side effects: Nausea and dizziness.
Not suitable for: women with high blood pressure or a focal migraine at the time.
Effectiveness: 95 per cent effective.
How it works: by altering the environment in the womb, making it difficult for the egg to implant.
What if I am too late? An IUD (intra uterine device) can be fitted up to five days after unprotected sex.Reuse content