Women are being invited to stock up on free supplies of the morning-after pill which will be sent to them by post.
The British Pregnancy Advisory Service (BPAS) has launched a service where women in London can request the pill over the phone and get it delivered free of charge to their home.
The charity says the Just in Case kit, which also includes condoms, will help women prevent unwanted pregnancy during the summer months.
The morning-after pill is most effective if taken as soon as possible after unprotected sex, preferably within 12 hours. But it can be taken for up to 72 hours after intercourse.
A BPAS spokeswoman said the kit is delivered to women once they have completed a telephone consultation with a nurse.
She said that "significant disruption" is expected in London during the 2012 Olympic Games, which could make it more difficult to access healthcare services swiftly if regular contraception fails.
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Tracey Forsyth, BPAS lead contraception nurse, said: "Our Just in Case kit means you have a back-up there when you need it, wherever you happen to be.
"The sooner you take emergency contraception the more effective it is.
"If you carry an umbrella in your bag or a spare tyre in your boot no-one would suggest you are hoping for rain or planning on a puncture. Having the morning-after-pill to hand is no different. It doesn't mean you're planning on taking chances, it means you're planning on protecting yourself when things don't go according to plan."
Women are advised to fill in an online form at www.morningafterpill.org.uk and the contraceptives nurse will call them back.
They will also be told how to take the pill and what to expect.
The BPAS spokeswoman said nurses are trained in spotting under 16s, who would be referred to a BPAS centre for a face-to-face consultation or another appropriate venue.