Doctors at Great Ormond Street hospital, London, are to continue gene therapy treatments for baby boys with a potentially fatal bone marrow disorder, despite two children on a parallel programme in France developing leukaemia.

Treatments were suspended between January and last month, but safety advisers believe the benefits of the experimental therapy still outweigh the risks if families opt for it for their sons after appropriate counselling.

Four babies and an adult in Britain have undergone the treatment in the last two years. The hospital said yesterday they were all well and being monitored.

Trials at the Necker hospital, Paris, on about a dozen patients, were suspended last year after one developed leukaemia. News of a second child in France developing a form of blood cancer early this year led to another safety review here.

A working group of members from two government advisory committees, on gene therapy and the safety of medicines, has called on the government to commission new research into the safety of using engineered viruses to deliver corrective genes.