Bradford GPs have been told to stop sending non-urgent blood tests to a laboratory because its computer system has become infected by a virus.

The problem at the Britannia House laboratory in Morley is connected to a major virus which has hit computers at Leeds Teaching Hospitals.

More than 80 GPs' surgeries in Bradford and the city's Royal Infirmary have been told that the laboratory, which is linked to the Leeds hospitals system, is only able to deal with urgent blood tests because of the problem.

It has meant test results can no longer be sent by the usual method of email, and have to be phoned through or posted instead.

The virus - known as Nachi or Welchi - is one of a number which have afflicted systems at organisations, including other local businesses, this week, and leaves computer screens blank.

It infected around 1,000 computers at the Leeds Teaching Hospitals Trust yesterday and staff were still trying to get the system up-and-running again today. A spokesman for Bradford Hospitals stressed that the test results themselves were not affected and no patient records had been lost as a result of the virus.

He said that the delivery of some test results had been prioritised as a result of the difficulties.

But hospitals in the Leeds area, including Wharfedale General in Otley, experienced major difficulties.

At one stage, hospitals in the trust considered cancelling appointments and operations because of the chaos.

A spokesman said: "Hopefully, patients won't have noticed any difference because we were putting all the necessary procedures in place. This has mainly been an administration issue but we may have some catching-up to do when things get back to normal."

He admitted that the trusts were reliant on the computer system and would reassess the situation in light of the problems.

The virus is believed to have stemmed from the so-called Blaster worm.