The study, published in the journal Thorax, was based on more than 3,000 children whose respiratory health was tracked from birth to 11.5 years of age.

The children were all participants in the Avon Longitudinal Study of Parents and Children (ALSPAC), which has been following the long-term health of 14,000 children and their parents.

The parents were quizzed annually on symptoms of wheezing among their offspring and whether a doctor had diagnosed asthma in their child by the time s/he was 7.5 years old, but not before the age of 3.5 years.

Parents were also asked to assess their children’s TV viewing habits from the age of 3.5 years, and these were subsequently compared with those of their symptom-less peers.

The amount of time spent in front of the box was used as a proxy measure of sedentary behaviour, because personal computers and games consoles were not in widespread use at the time (mid 1990s).

The prevalence of asthma among children at the age of 11.5 years, who had no asthmatic symptoms when they were 3.5 years old was 6 per cent.

However, children who watched TV for more than two hours a day were almost twice as likely to have been diagnosed with asthma as those who watched the box less.