The risk of epidurals and spinal anaesthetics to expectant mothers and patients undergoing surgery may be overstated, a study suggests.

An epidural is a form of anaesthesia whereby drugs are injected through a catheter, blocking nerves near the spinal cord and causing loss of pain and sensation.

Researchers at Bath's Royal United Hospital analysed the complications from the 700,000 pain-killing injections given each year.

They found the risk of harm was at least as low as one in 23,000; 10 times less than tends to be estimated.

The Bath team were given data from all the hospitals in the UK and found between 14 and 30 patients were permanently harmed.

Researchers could not be exact because in some cases the cause of injury was not totally clear.

The risk of paralysis is two to three times lower than this, and the risk for women who are giving birth is even lower - estimated at around one in 80,000.

The study confirmed previous findings that the risks associated with surgical epidural use are greater than when it is used during childbirth.

However, Dr Tim Cook, a consultant anaesthetist at the Royal United Hospital in Bath, said that these figures are still lower than many previous estimates of risk.

'It has been known for a long time that these complications occur more often after surgery,' he revealed.

'The reason is likely to be that many of these patients are elderly with medical problems and that the process of undergoing surgery itself increases risks.'