Amy Winehouse may appear to be struggling with drugs and drink, but the singer's selling power remains undimmed. It is almost two years since Universal Music, her record company and the market leader, released Back to Black in the UK, yet the album was still Universal's bestseller worldwide in the first half of this year. The album outstripped Duffy's debut (second on the Universal hitlist) and Lil' Wayne, the rapper whose album Tha Carter III sold more than one million copies in its first week in the United States - the first time that had happened in three years.

Winehouse's Back to Black sold more than 11 million copies internationally, while her first album for Universal, the less well-known Frank, released in late 2003, logged in at more than two million. Her personal fortune is now estimated to be £10 million and she is the bestselling new act since EMI's Norah Jones topped 20 million in 2007 with Not Too Late.

The durability of Winehouse's sales helped the Vivendi-owned Universal Music to hold the drop in revenues at the company's recorded music division to 3 per cent in the first half of the year, at €1.7 billion (£1.4 billion). This is on a par with Warner Music, the only other music major to report half-year figures - but better than the overall market.

Album sales in the United States, the world's largest market, were down 11 per cent by volume in the first half, even when paid-for digital downloads are included. Volumes in Britain, the third-biggest market after Japan, are down about 7 per cent. It has proved impossible to compensate for lower volumes through increased prices.

Universal, at least, has albums from U2 and Take That to look forward to in the run-up to the Christmas season. But for Winehouse, there is little sign of a new album. The singer has got some new material - when summoned for a crisis meeting with Universal's international boss Lucian Grainge this year, she tried to impress him with a song - but she continues to play summer festivals (or in the case of a date in Paris last week, not turn up) and has not been anywhere near a recording studio.

Universal can hardly complain, given the longevity of Back to Black, but there is little doubt that the record company is keen for her to produce a new album before the public finally tires of the endless tabloid tittle-tattle. Even if it were hastily recorded, at best a new album from the 24-year-old would not appear for a year.