John Profumo, whose highflying political career in Britain ended in a cold war scandal of sex and espionage that gave way to a lifetime of atonement, died about midnight on Thursday. He was 91.

For a land that has since become renowned for ministerial misbehavior, Mr. Profumo's imbroglio in 1963 set a standard, and became known in newspaper headlines as the Scandal of the Century.

It helped bring down the Conservative government to which Mr. Profumo belonged and put an abrupt halt to his political ambitions, which, some said, could have made him prime minister. The scandal titillated millions of Britons with tales of misbehavior that had the hallmarks of a salacious thriller: nobility and spies, call girls and country estates, sex and suicide, guns and lies.