Normal childbirth has for the first time become a minority activity in Britain, marking a new milestone in the history of medicine.

Figures published by the Department of Health show that less than half of new mothers - 45 per cent - had a spontaneous labour and delivery in 2001-02 with the remainder experiencing some kind of medical intervention. This compares with 53 per cent who had a normal birth in the last set of statistics covering the three years from 1998-99 to 2000-01.

The finding means that a spontaneous delivery can no longer be regarded as the "normal", or majority, way of giving birth. Medical interventions during labour and birth, include induction to start the process, anaesthesia (epidural or general), the use of instruments such as forceps or Caesarean section. Ordinary pain relief, given by a midwife, and including pethidine and gas and air is not counted as a medical intervention.

Intervention in childbirth has caused increasing disquiet among patient groups, medical organisations and politicians. The biggest single change of the last 20 years has been the doubling in the Caesarean rate, driven by fears of litigation and a demand from some women for what they see as a convenient, pain-free method of delivery.

The latest figures show that in 2001-02, the Caesarean rate for England was 22.3 per cent compared with 9 per cent in 1980. The rate is continuing to rise despite efforts to curb it.

The Royal College of Obstetricians conducted a national survey of Caesareans in response to the soaring popularity of the operation. It showed that half of consultant obstetricians were worried that the rate was too high in their own units. One private maternity unit had a rate of 56 per cent.

The National Institute for Clinical Excellence is drawing up guidelines for Caesareans. They will set out the circumstances in which a Caesarean should be performed but are expected to say that the woman's choices should be taken into account.

The Royal College said the trend towards elective Caesareans among middle-class women was accelerating. Peter Bowen Simpkins, vice-president of the college, said: "We feel female pressure for Caesareans is becoming more and more intense. Women are asking for it. They don't want a tear or the other side effects of a normal delivery and they are opting for a Caesarean. Professional women are keen on saying they want to come in on a particular date to have their baby."

"With the new spinal anaesthetics there is now wonderful analgesia, the women have no stitches and Caesareans are seen as safer. But the truth is there is unquestionably higher morbidity with Caesareans."

Mr Bowen Simpkins said it was "distressing" that the proportion of women having normal deliveries had fallen to 45 per cent. He blamed a shortage of senior consultants which meant women in labour were left in the charge of junior doctors who were less experienced and likely to intervene sooner to prevent things going wrong. "We are facing huge problems on recruitment," he said.

Maggie Blott, a consultant obstetrician, said: "Midwives are leaving because they are worried about the medicalisation of labour ... We need to put our house in order and recruit more midwives so women have one-to-one care. Mary Newburn, of the National Childbirth Trust, said the increasing rate of intervention was "disappointing but not surprising" and raised questions about the way labour was managed.