The investigation, by the Confidential Enquiry into Maternal and Child Health (CEMACH), comes amid growing unease among clinicians over a legal ambiguity that could see them being charged with infanticide.

The number of terminations carried out in the 18th week of pregnancy or later has risen from 5,166 in 1994 to 7,432 last year. Prenatal diagnosis for conditions such as Down’s syndrome is increasing and foetuses with the condition are routinely aborted, even though many might be capable of leading fulfilling lives. In the past decade, doctors’ skill in saving the lives of premature babies has improved radically: at least 70%-80% of babies in their 23rd or 24th week of gestation now survive long-term.

Abortion on demand is allowed in Britain up to 24 weeks — more than halfway through a normal pregnancy and the highest legal limit for such terminations in Europe. France and Germany permit “social” abortions only up to the 10th and 12th weeks respectively.

Doctors are increasingly uneasy about aborting babies who could be born alive. “If viability is the basis on which they set the 24-week limit for abortion, then the simplest answer is to change the law and reduce the upper limit to 18 weeks,” said Campbell, who last year published a book showing images of foetuses’ facial expressions and “walking” movements taken with a form of 3-D ultrasound.

Jessen, a musician from Nashville, Tennessee, was left with cerebral palsy but is to run in the London marathon next April to raise funds for fellow sufferers.

“If abortion is about women’s rights, then what were my rights?” she asked.

“If people are going to talk about abortion, then it’s important for them to know that these are babies that can be born alive and survive.”