A Darlington relative of a patient who may have been accidentally infected with an incurable brain disease last night hit out at the NHS for keeping them in the dark.

She spoke out after it was revealed that 24 people who had brain surgery at Middlesbrough General Hospital may have been infected with Creutzfeldt-Jakob Disease through tainted surgical instruments.

As Government experts appealed for calm, angry families said they should have been told earlier.

Although hospital bosses were alerted to the danger nearly three months ago, some patients had no idea they might have been exposed until they read The Northern Echo yesterday.

One woman from Darlington, whose daughter-in-law is one of the 24 patients, said: "We are very angry that those people who have been affected were not told first. It's an appalling oversight."

The woman, who asked not to identified, said that those affected should have been informed much earlier and she criticised the NHS response.

By the time her daughter-in-law received notification in the post yesterday that she was one of the 24, a telephone helpline set by hospital officials was already jammed.

"I tried and tried to ring the helpline to get more information but just couldn't get through," she said.

By last night the special telephone line had taken 150 calls. Patients are being told the risk of infection is "extremely low" but one admitted: "It is terribly worrying."

As the implications reverberated around Westminster, Chief Medical Officer Professor Sir Liam Donaldson ordered an investigation.

It follows an exploratory brain operation on July 19 on a woman patient who was not suspected of having the rare fatal disease.

A neuropathologist at the Teesside hospital who wanted to rule out the condition sent a sample to the national CJD centre for analysis.

When a positive CJD diagnosis was confirmed on August 8, the hospital ordered that the instruments be set aside. By that time they had been used on another 29 patients.

But it was only on Tuesday night that the trust was given the go-ahead by the national CJD centre to warn 24 of the patients deemed to be in potential danger. Patients will want to know why it took nearly three months to warn them they might have been exposed to CJD.

There are also concerns that many patients only learned about the scare through the media.

Bosses at South Tees Hospitals NHS Trust have insisted they followed correct procedures, despite criticism from the Department of Health over the length of time it took to take the instruments out of service.

The trust also insists it could could not approach patients until permission was given by the CJD surveillance unit.

Dr Paul Lawler, medical director for the South Tees trust, said: "There may be a weakness in the system but it is not our weakness."