UP to 29 patients may have been exposed to the deadly brain disease CJD because of a hospital blunder, it was revealed last night.

Department of Health officials said that the patients were put at risk at Middlesbrough General Hospital when contaminated instruments were used.

In what they admitted as "an appalling incident", officials revealed that all had been operated on using the same surgical instruments as a patient who was later confirmed as suffering from the rare brain disease.

An urgent inquiry is now under way into how instruments which should have been quarantined until the patient had been confirmed free of CJD were re-used - a practice banned under NHS guidelines, which the Department of Health described as "crystal clear". All the affected patients have now been contacted to return to the hospital, The Guardian reports today.

The discovery was made after the original patient had a brain operation on July 19 and the diagnosis was confirmed on August 8.

However, in the intervening days, 29 patients were operated on with the same equipment - equipment which was eventually withdrawn from use after the diagnosis was confirmed.

Last night, hospital officials said the patient recall was now taking place as a "precautionary measure" because of what was described as a "theoretical risk" of the spread of the disease.

A spokesman for South Tees Hospitals NHS Trust said last night: "The Trust immediately made inquiries with the health authority, public health department and the Department of Health's CJD surveillance unit.

"Since then, we have been working closely with the CJD surveillance unit to look at any possible risk to these patients, though it must be stressed, it is extremely low."

The Department of Health spokesman said its guidance on the handling of instruments possibly exposed to CJD had been in place since 1999.

He said the guidelines to NHS trusts were there to ''prevent the avoidable and unnecessary exposure to this disease''.

He added: ''It appears that the Trust concerned has failed to do so. Twenty-nine patients were operated on with some of the instruments used. The instruments were withdrawn once CJD was confirmed.

''The Trust is now, as a matter of precaution, informing those patients and their families. We do not know what the risk is.''

Sporadic Creutzfeldt-Jakob Disease (CJD) accounts for about 85 per cent of all cases of the illness and, although it can prove fatal, it can also have an incubation period of up to 20 years.

It is not to be confused with variant CJD which is the human form of BSE and potentially linked to contaminated meat.

The hospital said it had been advised not to recall patients until such time as further guidance was received from the Department of Health - guidance which was finally received yesterday.

Doctors are now in the process of meeting every one of the 29 patients to fully explain their unfortunate circumstances. A hospital spokes-man said: "We appreciate the distress and concern this news may cause to these patients, their families and the public at large, and we are in the process of setting up a helpline."

Clive Evers, of the CJD Support Network, said: ''Clearly what is happening is that good, solid guidance is produced, bringing together a range of professionals, and it is not being disseminated, it is not being taken seriously, it is not being publicised enough to the people who need to have access to it.

''That's the lesson that has to be learnt."

Dr Evan Harris, health spokesman for the Liberal Democrats, said: ''It seems as if a serious error was made in exposing subsequent patients to an avoidable and theoretical risk of infection of CJD.

''What data there is suggests that the risk is highest for the first six patients in descending order, as the instrument would be cleaned and sterilised after each use."