Surgeons are drilling holes in the wrong side of people's heads during brain surgery despite a warning issued three years ago.

So-called wrong site surgery has been a consistent problem in the NHS and in some cases patients have died as result of having the wrong organ removed.

In 2005 the National Patient Safety Agency issued an alert to all neurosurgical units after an audit found there was no standard method of identifying which side the patient was to have surgery with some units marking with pen the side to be operated on and others marking the side not to.

Since the alert the NPSA have had another 15 reports of incidents in nine of the 36 neuro centres where surgeons have begun brain surgery on the wrong side of the head.

Another alert has now been issued saying it is still a problem.

The brain surgery incidents are among 56 wrong site surgical mistakes reported to the NPSA during 2007 and another 654 reports related to operating list errors where the wrong patient or the wrong operation had been planned.

None resulted in the death of the patient but all were avoidable and in some cases the mistake was not realised until holes had already been drilled through the skull.

The burr holes are necessary to relieve pressure in the skull where the brain has swelled as a result of disease or trauma or to access the brain for delicate surgery.

Around 3,000 such operations are carried out each year in the NHS in England.

Chief Medical Officer Sir Liam Donaldson has said wrong site surgery should never happen and hospitals may face penalties.

Kevin Cleary, Medical Director of the NPSA said: "These incidents reveal that staff are not always following best practice procedures for pre-surgery checks and this is causing avoidable errors to occur in our neurosurgical units in the NHS.

"The NPSA has identified common problem areas, such as staff failing to mark the patient to show the side for surgery before they go into theatre, vital information not being included on the operating list and patient consent form, and staff failing to challenge the surgeon once they notice that surgery has started on the wrong side.

"Our Rapid Response Report gives explicit guidance on the marking and checking procedures that the neurosurgical team should follow prior to commencing surgery. This is in line with the latest guidelines set by the World Health Organisation.

"It is a requirement that they are adopted in all neurosurgical settings."

Earlier this year the World Health Organisation Surgical Safety Checklist was launched and has been backed by Sir Liam.

It lists a series of checks that should be carried out to ensure the correct patient is in the operating theatre, the correct operation is about to be carried out and on the correct body part.

The checklist has been compared to the preflight checks that pilots carry out and Si Liam has been keen to ensure surgery follows similar standards.

John Black, President of the Royal College of Surgeons of England said: "Team work is vitally important in an operating theatre and every member of the team needs to be clear on the correct procedures to follow and to have the confidence to question the team leader at any point in an operation if they think there is a problem.

"This report builds on the work the College has done with the NPSA to give clear guidance on how you mark up a patient's body for neurosurgery.

"There are always improvements we can make and I encourage every member of the surgical team to report near misses or actual incidents so we can continue to work in partnership with the NPSA to ensure the best possible patient safety across the board."

Phillip van Hille, President of the Society of British Neurological Surgeons said: "Neurosurgery is committed to the highest standards of patient care and wishes to do everything possible to avoid wrong-side cranial surgery.

"The Society considers that appropriate preoperative marking may help reduce the risks of wrong-site surgery. The Society strongly supports the final preoperative ("time-out") check in theatre before patients are finally positioned and prepared for surgery."