In Britain every generation produces a national treasure, a lovable John Bull figure so English that he could not possibly be of any other nationality: first P.G. Wodehouse, then John Betjeman and now John Mortimer. Mortimer has delighted millions all over the world by writing seven television series about his gloriously larger-than-life fictional barrister, Horace Rumpole -Rumpole of the Bailey. He has also written novels, autobiographies, stage plays, film- scripts, short stories, television and radio plays, and newspaper articles -even an opera and a ballet.

He practised as a barrister for thirty-six years, defending husbands, wives, pornographers and murderers and starring as the 'Devil's Advocate' in several legendary obscenity and blasphemy cases in the 1970s to become a liberal hero of the Permissive Society. Laurence Olivier, John Gielgud and Alec Guinness appeared in his plays and he served on numerous worthy committees, including those of the National and Royal Court Theatres, the Royal Society of Literature and the Howard League for Penal Reform.

Yet despite Mortimer's huge success, fame, sexual conquests and knighthood there lurks beneath that genial 'champagne socialist' mask an unusually complex man who has been plagued by depression, doubt, insecurity and an irresistible urge to commit adultery.

Graham Lord, whose discovery that Mortimer had a secret son by the actress Wendy Craig forced Sir John to admit it publicly in 2004, has interviewed scores of his family, friends, mistresses and enemies to write a devastating biography that reveals the startling reality behind the cuddly image - a book that Mortimer at first encouraged and then tried desperately to censor, in vain.