BRITAIN'S opposition Labour Party leader John Smith died suddenly yesterday of a massive heart attack. The 55-year-old politician, who had an attack also in 1988, suffered chest pains at his London home at 8.05 am (3.05 pm Hong Kong time). He was rushed to hospital, but efforts to revive him failed and he died 70 minutes later with his wife, Elizabeth, at his side. Smith had adopted a rigorous fitness regimen and cut his weight from 95 to 76 kilograms, but medical experts believed the stress of running a political party was too much. Labour's deputy leader, Margaret Beckett, was announced as a stand-in leader ahead of a contest. As tributes poured in, normal parliamentary business at Westminster was scrapped for the day and the Scottish Tory Conference was adjourned ahead of a five-minute speech in praise of Smith. Prime Minister John Major spoke of his ''shock and sadness'' and said Smith had been an ''outstanding parliamentarian and leader of his party and his country''. Liberal Democrat leader Paddy Ashdown called him ''a man of honour''. The Queen sent a personal message of sympathy to his widow and three daughters. Hong Kong Governor Chris Patten said: ''He was a good and decent man, widely respected regardless of people's individual political opinions.'' Mr Patten was chairman of the Conservative Party when Smith was shadow chancellor. They clashed frequently during the election campaign, particularly over Smith's tax policies, but remained on cordial terms. Former Labour leader Neil Kinnock, replaced by Smith after the party's defeat in the 1992 general election, said: ''It is a devastatingly sad day. He was a fine man and a fine leader and this is just such an appalling shock and everybody will feel the deepest sorrow.'' Former prime minister Lady Thatcher described Smith's death as a ''dreadful loss, not only to his family but to his party and the country''. ''His courage and fundamental decency made him one of the best-liked political leaders,'' she said.