Even in a game known for its prodigies it was a momentous achievement. British chess was hailing a new child star yesterday after a boy aged eight took on England's number five grandmaster and won. In the most sensational result of the Mind Sports Olympiad in London, David Howell, British under-10 champion of Seaford, Sussex, defeated John Nunn, 44, player and author of world renown. The victory will convince the 150 nations of the world chess body Fide that Britain has a new star. Although it was only five-minute blitz chess, a race of moves against the clock, experts take this form of the game extremely seriously. All the olympiad blitz events have been won by grandmasters, and each offers £500 prize money. The audience of experts yesterday was too stunned to applaud when Dr Nunn resigned. But David, who learned the game at five, had already shown the promise of a Nigel Short. In a side event at the British Championships in Scarborough this month he defeated the top woman, Harriet Hunt, in a game that broke an age performance record that had stood since 1920. Dr Nunn won a gold medal for England at the 1984 Chess Olympics and wrote a best-selling book on openings. He was the victim of a prodigy 12 years ago when he tied a blitz match with Judit Polgar, then 11, who became the first woman to match the top men.