Three years ago, the National Patient Safety Agency concluded hospitals lacked a standard method of marking patients – with some doctors using a pen to mark the side to be operated on and others marking the side not scheduled for operation.

Since then, there have been another 15 reports of British surgeons beginning brain surgery on the wrong side of the head, The Daily Telegraph reported Saturday, noting none of the 15 patients died.

An estimated 3,000 such operations are conducted in Britain each year to access the brain for delicate surgery or to relieve pressure in the skull where the brain has swelled because of disease or trauma, the Telegraph said.

British hospitals face penalties if they do not adopt explicit surgery guidelines set by the World Health Organization, said Kevin Cleary, medical director of the Patient Safety Agency.

"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," Cleary said.

The World Health Organization Surgical Safety Checklist details procedures to ensure the correct operation is about to be performed on the correct body part, Cleary said. The checklist has been compared to the check list executed by pilots before takeoff.