An investigation has been launched after a hospital operated on four patients using equipment which had not been properly sterilised.

Eastbourne District General Hospital apologised last night for the "regrettable" blunder, which could have left the four open to infection.

Hospital chiefs said four trays of surgical instruments missed the second stage of a vital two-step sterilisation procedure.

The patients, who have not been identified, were contacted by senior clinicians who warned them of the potential risk and offered hepatitis B vaccinations. The operations took place last Wednesday and Thursday.

A hospital spokesman last night played down the danger to patients.

He said: "We are not talking about instruments that have got blood on them. They passed through the first part of the sterilisation process which had cleaned them. We are now investigating what went wrong.

"There is a system in place with five checks before equipment goes into the operating theatre and regrettably there was a human error."

The mix-up came to light after staff noticed a cleanliness marker on each of the four trays of instruments had not changed colour.

The hospital in Kings Drive, Eastbourne, said in a statement: "Those trays had been through a cleaning and disinfectant process but they did not complete the full sterilisation process. We have contacted the four patients concerned and apologised to them.

"Senior clinical staff have spoken in great detail to reassure them about the minimal risk of infection as a result of this regrettable action."

Eastbourne Hospital, which received one star in NHS league tables last week, is investigating what went wrong.