At least 20,000 excess Caesarean operations take place in the United Kingdom each year as surgical intervention in childbirth has grown sharply, according to latest figures.

Doctors and midwives have expressed alarm at the trend and the Royal College of Obstetricians and Gynaecologists (RCOG) has launched a national audit to discover the reasons behind it.

A preliminary audit carried out by researchers from Hull Maternity Hospital obtained Caesarean rates for 221 maternity units throughout the UK for 1997-98.It showed that the rate had risen from between 14.3 and 16.6 per cent in 1993 to between 18 and 19 per cent in 1997-98.

The World Health Organisation recommends that the maximum desirable level of Caesarean operations is 15 per cent of all deliveries. The number of operations in the UK in excess of this level in 1997-98 was 19,470. As some maternity units did not provide data, the 1997-98 figures "may well be an underestimate", the researchers say.

The figures were published in the British Medical Journal last month. Dr Stephen Lindow, a senior lecturer in perinatology at Hull Maternity Hospital, and colleagues obtained them from a manual search of returns to the RCOG.

Caesarean operations are controversial because they are determined on social as well as medical grounds. Doctors say a Caesarean section is a serious abdominal operation and that women take longer to recover from it than from a normal birth.But they also say demand from women for the operation is rising.

Dr Lindow said that 20,000 "excess" Caesarean operations did not mean there were too many. "No one would argue with a Caesarean rate of 15 per cent. But does that make 16 per cent bad?" he said.

"Caesarean rates are increasing but we don't know if that is a good or bad thing. I meet women on a daily basis who, in certain circumstances, opt for a Caesarean in preference to induction or an alternative method, especially if they have had a previous one."

The National Childbirth Trust, which is collaborating on the national audit with the RCOG, the Royal College of Midwives and the Royal College of Anaesthetists, said wide variations in rates were a matter for concern. Since 1993, Caesarean rates have been rising faster in England and Northern Ireland than in Scotland and Wales. Belinda Phipps, the trust's chief executive, said: "We are not asking for all Caesareans to be stopped. In many cases they are necessary for good clinical reasons. However, in our view rates have reached unacceptable levels and we want to know why."

Initial results of the audit are expected in November.