Thirty years ago, a group of four singers little known outside their native Sweden wowed the judges in the British town of Brighton to win the Eurovision Song Contest. Waterloo went on to top the charts in Belgium, Britain, Denmark, Holland and, not surprisingly, Sweden. It even reached sixth place in the difficult to crack United States market. It would be the first of several hits that would change the face of pop music. Waterloo has sold more than five million copies worldwide. A few months after Waterloo's successful international debut, Honey Honey became Abba's second million-seller on the continent. A year later, SOS returned the group to Britain's Top10 and America's Top20 lists. Abba also won over non-English-speaking markets. By early 1976, their rendition of Mamma Mia - title song in the musical hit that opens in Hong Kong on Wednesday - had topped the charts in Britain and Germany. Twelve more singles were released by the end of 1979, all of which reached Britain's Top Five. They included Fernando, which also topped the charts in Holland and Australia; Dancing Queen, their only No1 in the US; Knowing Me, Knowing You, a chart-topper in Germany; The Name Of The Game and Take a Chance On Me. The only group to have had more albums top the British charts through to the end of 1991 were The Beatles. As one of the best ideas to come out of Sweden since blondes, Agnetha Faltskog, Benny Andersson, Bjorn Ulvaeus and Anni-Frid Lyngstad - whose first initials resulted in Abba - were the first internationally successful pop group to sing in a language other than their mother tongue. If Abba is Sweden's most famous pop music export, the country's contribution to the worldwide musical scene is far greater than most music lovers realise. The Backstreet Boys, Britney Spears, Celine Dion, Christina Aguilera, Jennifer Lopez, N'Sync and Westlife have all recorded hits written and produced by Swedes.