Cancer patients are being recruited for the first British run trials of man-made tumour busting viruses.

About 20 volunteers will be involved in the early stages of the experiments, testing the safety and short term efficacy of the treatments, which researchers hope might eventually be able to combat 95% of cancers.

They believe that injecting genetically modified viruses into the bloodstream will provide an alternative to radiotherapy and chemotherapy, which can lose potency as cancerous cells develop resistance.

The tests, by scientists working for the Hammersmith Hospitals NHS trust at Imperial College, London, involve mod ifying viruses to work against tumours which have an inactivated version of genes that usually work against cancer.

Work is already advanced in the US on altering the adenovirus, a common cause of respiratory and eye infections, to fight cancers with an inactive P53 gene, including cancers in the head and neck, ovaries and bowel, and those trials have involved British patients.

However, the new research will involve using viruses to tackle a far wider range of cancers. They should kill the cancer cells but spare normal ones. "The idea is that if you make particular changes to one or two genes in native viruses you can make them less infective to normal cells but as infective or more infective to tumour cells," said Nick Lemoine, one of the researchers.

He and David Kirn, head of the viral and genetic therapy programme at the Hammersmith trust, outline the potential for the treatments in the latest Lancet Oncology medical journal.

Dr Kirn said: "Viruses have evolved over millions of years to express many of the qualities required for the ideal anti-cancer weapon.

"Viruses will target and infect very specific types of cell, multiply, cause cell death, and release more viral particles to go on and infect other target cells."