It is a guilty secret for many an exhausted parent: the distracting power of CBeebies. But allowing children under three to watch television can impair their linguistic and social development and puts them at risk of health problems, a psychologist told MPs yesterday.

Aric Sigman said letting young children watch as little as an hour and a half of television a day could put them at increased risk of health problems, including attention-deficit disorder, autism and obesity. The average child in Britain watches up to three times this amount - with the typical 11- to 15-year-old in front of a TV or computer screen seven and a half hours a day.

A growing body of research suggests putting infants and toddlers before a screen also causes irregular sleep patterns, while a study published last year found that children's resting metabolic rate decreased as the amount of TV they watched soared - meaning that physio-logical changes compounded the fact that they were not exercising.

Speaking to MPs and peers at a Westminster meeting yesterday, Dr Sigman said: "Between the ages of nought and three, particularly when children are acquiring language, their brains are going through rapid development and are being physically shaped, like a piece of clay, in response to what they are exposed to. It's called structural neuroplasticity.

"Key stages of development are language acquisition and social skills and if they're displaced at this stage, they may be irreplaceable." Dr Sigman, an associate fellow of the British Psychological Society and member of the Institute of Biology, said exposing children to fast-moving images at a very young age for a sustained time may inhibit their ability to sustain attention.

And children who were left for long periods with only a screen to interact with, not only had less time to speak to adults but also failed to develop social skills.

Dr Sigman, who has four children aged between three and 17, criticised programme makers who said television was educational and the government for not issuing rationing guidelines. He believes children under three should not watch TV, and those between three and seven should watch 30 minutes to an hour a day.

He told MPs at the conference organised by the pressure group Mediawatch-UK: "I was told by the head of BBC children's TV [Richard Deverell] that TV 'helps children get interested in the outside world'. The world around them gets them interested in the outside world.

"We are told children need electronic entertainment or they get bored. It is not true. Children have an infinite ability to entertain themselves which television seems to erode. What children are exposed to under the age of seven, and particularly under the age of three, is of paramount importance. It's really the under threes we're most concerned about and dramatically limiting the amount watched between three and seven."

A BBC spokesman said: "We agree that parents should monitor what and how much TV their children watch. The BBC does not make programmes for children younger than two and our pre-school programmes are made with children's development in mind."

A Department for Culture, Media and Sport spokesman said the government had no plans to introduce a recommended "daily allowance" rationing the amount of TV children watch.

One study, conducted by Cornell University last year, has suggested early exposure to TV could be a trigger for autism.

Primal screen

Dr Sigman's recommendations

· Children under three: no screen exposure

· Ages three to seven: 30 minutes to an hour a day

· Seven to 12: One hour a day

· 12 to 15: one and-a-half hours a day

· 16 and over: two hours

Programmes for under-threes

In the Night Garden

Teletubbies

Fimbles

Come Outside

Storymakers