Keeping children cocooned in ultra-clean homes away from other youngsters could trigger childhood leukaemia, a landmark study suggests.

A major new analysis by Britain’s leading leukaemia expert has concluded a deadly chain of events is set in motion when susceptible children are not exposed to enough bugs to prime their immune system at an early age.

Without sufficient immunity, if vulnerable youngsters catch even a relatively harmless virus like flu, the immune system malfunctions creating far more infection-fighting white blood cells than needed, causing leukaemia.

Professor Mel Greaves of The Institute of Cancer Research, London, said it was a ‘paradox of progress in modern societies’ that advances in cleanliness had caused such a devastating condition.

The study, which compiled 30 years of research into the cancer, raises the prospect that Acute lymphoblastic leukaemia (ALL) could become a preventable disease, which charities said was ‘enormously exciting.’

Simple steps such as allowing children to attend a day nursery so they come into contact with germ-laden youngsters, breastfeeding, outdoor play and not overly cleaning the house could all help boost immunity, the study suggests.

Professor Mel Greaves, Director of the Centre for Evolution and Cancer at The Institute of Cancer Research, London, said: “The research strongly suggests that ALL has a clear biological cause, and is triggered by a variety of infections in predisposed children whose immune systems have not been properly primed.