A controversial NHS pilot is providing the contraceptive pill to teenage girls without prescription in pharmacies.
Southwark and Lambeth, two inner-city areas in London with the highest teenage pregnancy rates, are the first to try the approach.
Experts have warned the government is struggling to meet its target of halving teenage pregnancies by 2010.
But opponents said there was no evidence providing the pill over the counter would make a difference.
Each local area has been given a target of a reduction of between 40% and 60%, for which responsibility is shared between the health service and local authority.
In England in 2007, 42 of every 1,000 girls under the age of 18 became pregnant - the majority unintentionally.
Half of those pregnancies ended with an abortion.
In Southwark the teenage pregnancy rate is 76 out of every thousand girls under 18.
The idea of training pharmacists to provide the contraceptive pill was first proposed two years ago by then Health Minister Lord Darzi.
He said there was strong evidence that better provision of contraception would significantly reduce unintended pregnancies.
Southwark PCT has been working for the past year to set up the project, developing a training course with King's College London that could be adopted if the pilots were replicated elsewhere in the UK.
Initially, three pharmacies have been given permission to offer contraceptive consultations to girls aged over 16.
At Ridgeway pharmacy they are getting ready to put up bold, colourful posters advertising in large letters "the pill without prescription".
For the past six weeks, young women asking for emergency contraception - the morning after pill - have been offered a private consultation on longer term alternatives.
So far around 50 have chosen to switch over to an oral contraceptive after being taken through similar checks to those which would be carried out by a GP.
Pharmacist Cuthbert Churinder has been trained by King's College.
He said the pilot had been surprisingly successful in the first few weeks - despite not being advertised.
"We do a lot of morning after pills here, I think the highest number in Southwark and Lambeth, about 220 consultations every month," he said.
"I think the PCT is doing the right thing to have chosen us to offer longer term and more reliable contraception to these young girls."
The pilot project is likely to attract criticism from those concerned that making contraception more readily available to 16-year-old girls might encourage them to have sex.
Mark Haughton, from the Christian Medical Fellowship, is not convinced providing the pill without prescription will make any difference to teenage pregnancies.
He said: "I'm not aware of any evidence this is going to be effective. It may be pouring petrol on the flames.
"Doctors and pharmacists are at the end of the chain. What we need to do is to work on the whole area of relationships - that is what is effective."
But Jo Holmes, from Southwark PCT, said it was taking a responsible approach to the reality that many teenage girls over the age of 16 were sexually active.
Focus groups run by the NHS with young women suggested that some found it difficult to approach their family doctor.
"I think the key thing about this service is that it is in a place which is accessible to young women," said Ms Holmes.
"They may already go there to buy cosmetics or medicines.
"In the GP surgery they sometimes worry they might bump into a neighbour or a member of their family."
The project has the approval of the Department of Health, which has previously used this approach of trying out potentially controversial policies in small-scale pilots.
The morning after pill became available in pharmacies nationally not long after pilot projects in Manchester provided enough data to allay concerns over safety.
There has been a reduction of 11% in the under-18 pregnancy rate since the target for England was set in 1998.
However, that is modest progress against a much more ambitious target.
If the pilot projects manage to make any contribution to reducing the rate they will be watched with great interest around the UK.