FORTY years ago today legislation that allowed abortions to be carried out in England, Scotland and Wales came into effect amid much controversy - now campaigners on both sides of the debate are gearing up for a new battle.

It is anticipated that MPs will next month have their say on whether the legal time limit for terminating a pregnancy should be lowered through amendments expected to be tabled to the Human Fertilisation and Embryology Bill, which is currently going through Westminster. It will be the first time politicians will have had a full opportunity to vote on this issue since the legal limit was cut from 28 weeks to the current 24 weeks in 1990.

The prospect of reducing the limit has provoked alarm among those wishing to safeguard the current arrangement, who say vulnerable women will be at risk if it is changed. Last week sexual health charity fpa launched a parliamentary campaign supporting the 24-week limit, with the backing of high-profile figures including comedian Jo Brand and author Dr Miriam Stoppard.

Meanwhile, Alive and Kicking, an umbrella group of pro-life organisations, is lobbying for a "substantial" lowering of the 24-week limit. Among those in favour is Nadine Dorries, a former nurse and Tory MP for Mid Bedfordshire, who is tabling an amendment to lower the limit to 20 weeks.

She said: "It has reached the point where, if we are a decent and humane society, should we be saying, when it gets to 20 weeks or pregnancy at five months, enough is enough? We don't abort from this point onwards as we know this baby could live if it was born and we know it will feel pain during this process of abortion."

She added: "I'm neither pro-life nor pro-choice, I'm just someone who thinks abortion is necessary in today's society, but 24 weeks is way too late."

In 1990, the limit was lowered in the wake of advances in foetal medicine, which meant babies born between 24 and 28 weeks stood a greater chance of survival. Two years ago, the world's most premature baby to live was born at just under 22 weeks: Amillia Taylor weighed just 10oz and measured 9.5in when she was born in a Miami hospital.

Another development which reignited the debate was four-dimensional imaging technology, which four years ago revealed the first pictures of foetuses at 16 weeks sucking thumbs and yawning and opening their eyes at 18 weeks.

The Scots obstetrician who pioneered the scans, Professor Stuart Campbell of London's Create Health Clinic, said he was fundamentally in favour of women being able to have an abortion. He backed a lower limit for terminations for "social" reasons, but said abortion should be permitted at a later stage for babies with severe abnormalities.

"I'd like it reduced to 20 weeks and ideally I think it should be 18 weeks. It is appalling to me to terminate babies that are so advanced in their behaviour patterns," he said. "The whole business of terminating is barbaric as well. I don't think we should be pulling out babies at such an advanced stage of development, many of whom could survive."

However, those in favour of the 24-week limit point to research published this month which found the number of babies surviving after being born so early had not increased significantly in recent years. The Epicure 2 study found that although survival rates among for babies born between 25 and 27 weeks rose significantly between 1995 and 2005, births at 24 weeks or less did not. Those who survived at 24 weeks were likely to suffer severe disabilities.

A joint statement by the British Medical Association, British Association of Perinatal Medicine, Royal College of Nursing and Royal College of Obstetricians and Gynaecologists, who all back retaining the current limit, stated: "There is no evidence of a significant improvement in the survival of pre-term infants below 24 weeks' gestation in the UK in the last 18 years".

Rebecca Findlay, of the fpa, claimed a reduction in the limit was only backed by a "small, very vocal" group of people who aimed to reduce women's access to abortion. She said: "For us, it is a very small group of vulnerable women who need to be protected. Only about 2% of all women who have abortions have one over 20 weeks and it is not an easy thing to have done in the first place."

Women who requested late abortions, she said, were often in the "most vulnerable and desperate" situations; such as homeless or abandoned by a partner. In other cases, tests for foetal abnormalities may not have taken place until the 17th or 18th week of pregnancy. If the limit was lowered, such women would be forced to carry on with an unwanted pregnancy, or access "backstreet" abortions, including buying abortion pills over the internet.

She said: "We know it will start happening, as we know the situation in Northern Ireland where abortion is only available in exceptional circumstances and we know how desperate women become if they can't access abortion."

In 1990 Lord Steel, the architect of the 1967 Abortion Act, backed reducing the limit from 28 to 24 weeks. But he is not persuaded it should now be lowered further. He said: "I think we politicians should be guided by the professional medical bodies who are united in believing the 24-week limit should remain, as there is no scientific evidence of viability before that."