We've all been there, and if you haven't your girlfriend has. The doctor's appointment shoehorned into a day that's already too busy. Minutes slipping past in the waiting room as you struggle to come up with a plausible explanation for why (and how, exactly) you've had unprotected sex.

Now, however, emergency hormonal contraceptives are to be available, not just on prescription from doctors' surgeries, family planning clinics and selected accident and emergency centres, but also over-the-counter at a chemist's.

Levonelle (the so-called morning-after pill) was removed from prescription-only control on January 1. Only then were Schering, its makers, free to start supplying the drug to the high street, with the result that while some pharmacies might receive stock as early as this week most of Britain's 15,000 chemists are not guaranteed delivery until January 30.

Those pharmacists who choose on moral or religious grounds not to sell it will be obliged to carry information about the nearest stockists. Boots say that all their pharmaceutical stores will carry supplies. Levonelle is not going to be difficult to find.

This has medical as well as convenience benefits. For while these pills can be taken up to 72 hours after unprotected intercourse, they are known to be more effective if taken sooner rather than later. (Levonelle is believed to prevent 95% of expected pregnancies if taken within 24 hours but only 58% if taken within 48-72 hours).

So no appointments, no waiting rooms, no uncomfortable questions? Almost. A slim little box containing two progestogen pills (to be taken 12 hours apart) is still not going to be as simple a purchase as suntan cream. There will be no slipping it quietly into your basket - you'll have to ask for it (tip: rather than make a foghorn decree of your nocturnal activities by demanding the "morning-after pill" try keeping icy composure and simply ask for Levonelle). And your boyfriend probably won't be able to buy it on your behalf either.

Before they sell the drug pharmacists are required by their professional body, the Royal Pharmaceutical Society (RPS), to obtain certain information from buyers. Expect a quick chat that ought to cover the following points.

First, pharmacists are supposed to satisfy themselves that their customer is 16 or over. Whether they go so far as to ask for proof of age is discretionary. They will also want to know that the pill is for you: RPS guidelines state that only in exceptional circumstances should Levonelle be sold to someone other than the patient.

The pharmacist will then seek to establish that you do need to take the pill; in other words, that you have had unprotected sex within the last 72 hours. Women ought to remember that they are not required to provide either details or excuses (although the pharmacist may make suggestions about suitable contraceptives); simply state the facts.

They will want to know if you could already be pregnant, in which case there would be no point selling this pill (though Levonelle does not appear to harm the baby if you do take it while already pregnant). So expect to be asked: Is your period late? If so, how late? Was the last one lighter or shorter than normal or unusual in any other way? Since the last one has there been unprotected sex at any time before this occasion?

The pharmacist ought also to check that you are not taking any medicine that might interfere with Levonelle and that you have no problems (such as vomiting or severe diarrhoea) that might affect its absorption. Finally, you will be asked if you are aware of having an allergy to levonorgestrel, the ingredient in Levonelle, or if you have a severe liver complaint, in which case this drug is not recommended.

Once you've got through that you'll have to pay £19.99 (significantly more than the standard prescription charge of £6.00 you'd pay after a visit to the doctor). With Levonelle, doctors say you don't have to worry about the side- effects - nausea and vomiting - notoriously associated with its predecessor "morning-after pill" the PC4.

A very small incidence of nausea and very occasional vomiting has been reported, says Professor Peter Bowen Simpkins, treasurer of the Royal College of Obstetricians and Gynaecologists. "But the recommendation is that it is taken with food and the incidence then is much reduced."

Levonelle is a progestogen-only pill. (Progestogen is a synthetic form of the hormone progesterone; PC4 contains progestogen and oestrogen). It's fine to take it if you miss your ordinary contraceptive pill. But it's worth remembering that the most dangerous time to miss a pill is not around day 13 (the most fertile point in the cycle), when you are substantially protected by the 10 or so pills already taken, but at the beginning of the packet, by elongating the pill-free week.

It is not related to the so-called abortion-pill, an anti-progesterone that induces menstruation and is only licensed in this country as a medical form of termination of pregnancy. Instead, Levonelle works in three ways. First, it stops or delays the ovaries from releasing an egg. Second, it prevents the sperm from fertilising an egg that might have been released. And third, "and this is the bone of contention," says Professor Bowen-Simpkins, "it may interfere with implantation of the egg in the womb". This is why some say taking Levonelle is tantamount to having a very early abortion.

Is there a level of usage at which, from a health point of view, worry might set in?

Professor Bowen-Simpkins says not that he knows of, "except for more than once a cycle because then you may get chaotic menstruation. The point is that we would be failing a patient who needed to take it so often by not giving them reliable contraception. After all, Levonelle is not 100% successful. It should only be seen as a back-up."

One grey area remains: whether emergency contraceptives can be stashed away in advance without resorting to telling fibs to a pharmacist. The RPS advises its members that supply in advance of need is not currently recommended and instructs them only to offer clients advice on where such a service is provided locally.

In fact, the British Pregnancy Advisory Service (BPAS) has been providing women with advance supplies of emergency hormonal contraception - first PC4, now Levonelle - for about 18 months for about £15 (which includes a consultation with a doctor) a go.

So perhaps the morning-after pill bought at the chemist the night before is not so very far away.