She also questioned whether it was as clinically effective as it was claimed to be.
Professor Glasier said it was important to see emergency contraception as a "back-up", not a method to reduce unintended pregnancy rates.
"It's a useful method for individual women, but as a public health measure it is not going to make a big difference to abortion rates. We have to have much more enthusiasm for methods which women use before they have sex," she told the BBC.
But Val Buxton, acting chief executive of Brook, a sexual health charity for young people, said: "Easy access to emergency contraception is an essential part of the picture, and abortion rates might be higher if it weren't for the fact that emergency contraception is more easily available than in the past."
Anne Weyman, chief executive of fpa - formerly the Family Planning Association - said emergency contraception was not the panacea but the health service was not giving women enough access to the contraceptive methods they needed.
"I think contraceptive services overall have had very low priority generally and at the moment we're actually seeing reductions because of the financial pressures in the NHS," she told the BBC.
"We're seeing closures of services in parts of the country which is going to mean that women don't get access to the methods they need, and we will see more unintended pregnancies."
A spokeswoman for the Department of Health said emergency contraception had never been heralded as the answer to rising abortion rates in the UK.
"Our policy has always been that safe sex, using reliable contraception on a regular basis, is the best way for women to protect against unwanted pregnancy."