The laptops contain information about some 20,000 patients, including their names, date of birth and postcodes, a spokeswoman for St George's Hospital, in Tooting, south London, said.

She said: "The Trust has written to every patient, apologising for the potential risk to their confidentiality.

"All data on the laptops was password-protected and personal information such as postcode was hidden, although the patient's name and hospital number was shown.

"The Trust acknowledges that patient data should not have been stored on laptops. This was done as a temporary measure because of a problem with the computer network.

"However, the laptops were in a secure area under lock and key. The data was being used to monitor and reduce waiting times at the hospital."

The laptops were stolen from offices in the Atkinson Morley Wing of the hospital between the evening of Friday June 6 and the morning of Monday June 9.

The spokeswoman said: "The laptops were stored in a secure room in a locked cabinet which appears to have been broken into by force."

The theft was discovered on Monday morning and the police were contacted. The spokeswoman said the hospital trust has begun its own investigation.