The online questionnaire for the heritage and conservation charity found that just 53% of the 1,651 10- to 12-year-olds who took part were able to identify an oak leaf, while half could not tell the difference between a bee and a wasp.

One in three survey failed to identify a magpie and only 47% correctly named a barn owl. A third failed to recognise a Red Admiral, Britain's best-known butterfly

In contrast nine out of 10 were able to correctly name Doctor Who's enemies the Daleks and a similar number recognised Star Wars' Jedi grand master, Yoda.

The survey is part of a National Trust campaign launched in London today aimed at encouraging families to spend more time together outdoors.

Television naturalist Nick Baker said: "It's a sad modern phenomenon that has left many of us, and in particular the younger generations, disconnected from the natural world.

"In an age where Nintendos and Playstations compete with tree climbing and pond dipping; the virtual world is winning.

"With more kids better able to identify a fictitious alien than our national tree, the Oak, something needs to be done."

Starting in London today, the trust is taking a flavour of the outdoors to major cities across England in the form of a specially designed garden on an open top double decker bus.

Entitled The National Trust Bus to Space, the tour aims to remind families that high quality outdoor space is only ever a short journey away, regardless of where they live.

National Trust spokeswoman Laura Brown said: "We want to let people know that they are no more than 45 minutes from a National Trust site wherever they are in the country, so there is ample opportunity to get and about and enjoy open space all around us.

"People are aware of National Trust houses but there's also lots of parkland and country estates that people can visit.

"The bus will park up in key city centre locations in Birmingham, Manchester, York and Bristol. The bus is quirky and very visual so we're hoping to attract lots of people on board and encourage them to go out and explore nature as a family.

"We will be handing out our summer planners which list an event for every day of the summer holidays at National Trust properties in each region. There will be lots of great family events going on such as bug hunts, nature trails and safaris."

National Trust conservation adviser Matthew Oates said: "Natural beauty and wildlife are vital to us. We are part of nature; we need it, and we need the beauty, wonder and laughter it offers us."

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