IF you thought the single was a thing of the past, think again. After dipping dangerously in the early 1990s, singles sales have been rising in the UK since 1992, when 52 million units were sold, to 87 million in 1997. Last year's figure, of course, was distorted by what is known in the business as "the Elton John effect" - Candle In The Wind 1997 was certified as nine times platinum after selling an extraordinary five million copies - and while singles sales have not increased across the board, with cassette singles in apparently irreversible decline and the seven-inch virtually extinct, CD singles and vinyl 12-inch are doing very nicely indeed. It's undoubtedly true that singles aren't what they used to be - today's CD singles usually offer three tracks, some of which may be live, or remixed, versions of songs which don't exist in any other form, giving them a touch of collectibility. Since 1995 the number one single in the charts has been clocking up average sales of over 100,000 copies a week - though to reach number 75 in the charts last year, all you had to sell was 2,000-odd copies, a figure designed to give good cheer to garage bands everywhere. Over a quarter of singles sold are bought on Saturdays, the vast majority by 15 to 24-year-olds.