The Birth Control Trust, with the backing of MPs, peers and family planning groups, is pressing for the drug to be taken off the prescription-only medicines list.
Britain currently has the worst record in Europe for unwanted teenage pregnancies, with 7,500 under-16s becoming pregnant each year, half of whom have abortions.
Lack of awareness and difficulty getting hold of the drug account for much of the problem, according to Ann Furedi, director of the trust.
She says 70 per cent of abortions could be prevented if women used "emergency contraception". The term "morning after" adds to confusion, as the pill can be taken for up to 72 hours after unprotected sex.
Ms Furedi said: "We believe that women are sensible and capable of reading labels and following instructions.
"The resistance to making it available for sale is partly because women are seen as being incapable and not competent of making a sensible judgement.
"There also exists an element of schizophrenia in that they want to promote use and reduce the number of abortions, but there is a reluctance because it can be seen to allow for unprepared for and unplanned sex. It is a moral issue.
"We want emergency contraception to be available off prescription so women can buy it like other pharmacy products. You don't wait until you have a headache to buy aspirin."
Results of a project in Washington in which pharmacists are issuing the drug have shown that half the women using the service said that without such easy access they would have simply waited to see if they were pregnant.
Ms Furedi said: "This shows that women don't use the morning-after pill because it is such a hassle to get."
A survey earlier this year carried out on behalf of the Contraceptive Alliance, an agency set up by the Family Planning Association and the Health Education Authority, said that almost half of all pregnancies in Britain are unplanned and one in five results in abortion.
The campaign, championed by the Liberal Democrat MP Jenny Tonge, begins on 11 June, when supporters will meet to discuss the possibility of putting down an Early Day Motion to reclassify the drug.Reuse content