A DOCTOR and a surgeon may be sitting on a potential goldmine after predictions that their invention could be prescribed on the NHS.

Thousands of the Virulite light therapy units have been sold since the North-East doctors launched their cold sore treatment last October.

The figure is likely to be boosted with the launch of an advertising campaign in a national newspaper - in time for the peak summer season for cold sores.

With a success rate of 99.8 per cent the hand-held plastic gadgets are likely to transform the treatment of painful mouth sores.

Now the doctors - Gordon Dougal, a GP from Peterlee, east Durham, and Jim Haslam, an eye specialist at Darlington's Memorial Hospital - are carrying out more scientific trials to confirm the device's effectiveness against cold sores and whether it provides a long-term cure.

Dr Dougal, who holds an electronic engineering degree as well as a medical qualification, said he was confident that the results would be positive.

"Once we have got that I am pretty sure that we will be able to get Virulite on NHS prescription, hopefully in a year or two," he said.

Dr Dougal and Mr Haslam have filed a patent for their invention and have formed a business partnership to develop a range of light therapy products, after Dr Dougal discovered that a narrow waveband of infrared light has powerful therapeutic effects.

The first fruits of the new technology is Virulite CS, which can clear up cold sores in half the time taken by conventional ointments.

Made in Hartlepool by Stadium, the device, which is about the size of a mobile phone, delivers a three-minute dose of infrared light to the site of the cold sore.

The doctors believe the light treatment works by strengthening the protective membranes around human cells, making it more difficult for viruses to penetrate them and exposing the viruses to an enhanced local immune response.

After investing what is believed to be a six-figure sum in researching and developing the cold sore treatment they are now looking to extend light therapy into new areas.

Dr Dougal believes that potentially life-threatening conditions, such as viral meningitis and viral myocarditis, may one day be treated by light therapy.

While illness caused by bacterial infection can usually be treated by a range of antiobiotic drugs there are far fewer antiviral drugs available to treat disease caused by viruses.

Dr Dougal said he was surprised that 0.2 per cent of users contacted by Virulite said that it did not work for them. But he added: "No cure is uniformly effective."

Virulite CS is available via the website, www.vsc.eu.com, or by ringing 0800 0523939.