Experts have said that some massively multiplayer online games, in which players battle enemies for weapons and rewards, are as addictive as crack cocaine.

Dr Richard Graham, a consultant psychiatrist at the Tavistock Centre in London, is so concerned that he plans to provide online therapy for youngsters who are spending so much time playing these games that they have lost touch with the real world.

A recent report by Sweden’s Youth Care Foundation described World of Warcraft as “more addictive than crack cocaine”. The game, which attracts almost 12 million players every month, is set in a fantasy environment, with users taking on the characters of dwarves, elves and wizards, interacting with other players throughout the virtual world.