Teenage girls are missing out on formative social activities and sports because they are addicted to their phones, a study found.

Two in five 15-year-old girls said they hardly ever leave their bedroom except to go to school, while one in five now spends no evenings out with friends during a typical week.

The Centre for Social Justice (CSJ) found that more than 250,000 15-year-olds in total across England now spend most of their time in their room.

That's a 50 per cent increase across both sexes since 2002.

One Year 8 girl told researchers: 'Since I got my new phone I don't want to come out my bedroom, and I've been more short-tempered and not feeling as energetic and active as I used to be.'

Sports and outdoor hobbies have also been replaced with sedentary screen time. 

Half of teenage girls said they avoid school sports because they worry they will not be good enough, compared with 38 per cent of boys.

In a report called Inactive Nation: Getting England's Teenagers Moving, the CSJ found girls' increasingly isolated lifestyles are detrimental to their physical and mental health.

Tabby Fitzgerald, Senior Researcher at the CSJ, said: 'Too many teenage girls are retreating into their bedrooms and onto screens while the independence that should be part of coming of age slips away. 

The answer is not just to restrict social media, but to put something better in its place.

'Sport and physical activity are good for our health, our resilience and for the friends we make along the way.'

One in five girls said their school offers no physical activity they enjoy, while seven in ten said they would be more active if there was a wider mix of sports at school.