A campaign is being launched to encourage children to surrender 30 minutes of screen time a day to head for the great outdoors.

The newly formed Wild Network – a collaboration of nearly 400 organisations - is attempting to attract youngsters away from television and computer screen and into fields, woods and parks.

Organisers say it is the UK's biggest ever campaign to reconnect children with nature and outdoor play, and claim it could help improve fitness, mental alertness and general wellbeing.

A documentary film, Project Wild Thing, will herald the launch at more than 50 cinemas across the UK from Friday. It looks at the increasingly fragile link between children and nature.

Members of the network include the National Trust, RSPB, Play England and the NHS sustainable development unit.

Andy Simpson, chairman of the Wild Network, said: "The tragic truth is that kids have lost touch with nature and the outdoors in just one generation.

"Time spent outdoors is down, roaming ranges have fallen drastically, activity levels are declining and the ability to identify common species has been lost."

Suggestions of how to get more time in nature include collecting conkers, camping or snail racing, and observing autumn colour on trees.

From January, the network will aim to make suggestions to politicians on how government can do more to get children muddy and bright-eyed.

This is not the first time the message of less screen, more play has been brought up. Children in the 1980s were entreated to do the same by the BBC TV series Why Don't You, which somewhat confusingly called on its viewers to "switch off your TV set, and go do something less boring instead".