A teenager who alarmed his parents by starting to write a novel in the middle of revising for his A-levels astonished them yesterday by getting a £50,000 advance for the book.

The money, thought to be a British record for his age, is part of a deal signed by the publishers Simon and Schuster for Anselm Audley's fantasy story Heresy.

The agreement includes publication of his next two novels "when he finds time to write them". For the icing on the cake is that Simon, now 17, got A grades in his three exams and is waiting to read history at St John's College, Oxford.

He embarked on Heresy, set in an alternative world governed by religion, while studying A-levels at Millfield school.

He said: "My parents were a bit worried at the time. They are delighted now. They were as stunned by the news as I was".

His path was initially smoother than most authors because his mother knew the literary agent James Hale, who suggested revisions in the story. But friendship had nothing to do with the speed with which Simon and Schuster accepted the typescript from Mr Hale.

"His book will definitely earn back the advance," John Jarrold, the firm's science fiction publisher, said last night after buying world English rights. "He is the best young fantasy writer I have come across in 13 years in publishing. He is an absolute master of characterisation with a sense of place that is remarkable for a writer of any age. His use of religion and politics can be compared to masters of the genre."

Mr Hale said: "He matured enormously between the ages of 16, when he began writing, and 17. It is a fully fledged, wonderful novel."

Anselm, who lives in Wiltshire, is currently studying for two more A-levels at a sixth- form college in Wiltshire.

His older record-setting rivals include:

•Richard Mason, 20, an Oxford student who last year sold his first novel, The Drowning People, for £200,000.

•Jenn Crowell, 19, an American who was paid £200,000 by Hodder in 1997 for the British rights to her love story Necessary Madness.

•Bo Fowler, a graduate of Malcolm Bradbury's creative writing course at the University of East Anglia, who received £140,000 from Jonathan Cape for his satire Scepticism Inc and another novel in 1998.