With a final flourish of his magic wand, Harry Potter, teenage wizard and hero for the modern age, has delivered a bumper farewell gift for his publisher Bloomsbury, an estimated £70 million in sales in Britain and English-speaking markets outside the United States.

Harry Potter and the Deathly Hallows sold a record 2.65 million copies in the first 24 hours after its July release in the UK and helped the book publisher to double its revenues to £150.2 million for the year ending in December.

But if Bloomsbury was celebrating the figures published yesterday, then it did so quietly. With no new Harry Potter titles to follow, his creator JK Rowling having decided to move on to new challenges, Bloomsbury has been hit by worries about whether it can continue to grow. In December 2006, the company issued a severe profits warning as non-Potter revenues on books such as autobiographies of David Blunkett and Gary Barlow, the Take That singer-songwriter, failed to come through.

Bloomsbury now faces a future in which it is turning for growth to “new business areas in specialist publishing” through deals such as producing reference materials for the Qatar Financial Centre Authority - as well as publishing established authors such as Khaled Hosseini and William Boyd.

Nigel Newton, the chief executive, said that Bloomsbury was “well positioned for the post-Harry Potter era”. He said that the business had cut £1.75 million of costs and had identified a further £780,000 of savings.

The publisher does not break out exact figures for Harry Potter sales, but it did say that turnover in its children's division had increased 261 per cent to £98.2 million from £27.4 million in 2006, a year in which there was no new Harry Potter title. The company said that the “main contributor” to the £70.8 million improvement was sales of Deathly Hallows. In Germany, where Bloomsbury released the book in English, a million copies of the seventh of the young wizard's adventures were sold despite the language barrier.

Net cash on the balance sheet has doubled to £48 million at the end of the year, although a substantial chunk of that is due in royaltes to Ms Rowling.

Richard Menzies-Gow, an analyst with Dresdner Kleinwort, said that, while the company had done a lot to bed itself down since the profit warning, it might have trouble impressing investors.

“It won't be easy getting people excited if what's left is a low-growth business,” he said. “The key will be using the cash aggresively to increase dividends, or make acquisitions.”

Pre-tax profits improved to £17.86 million, from £5.2 million. However, the advance paid to Ms Rowling and other related costs meant that gross profit margins after royalty payments fell to 39.4 per cent, from 48.4 per cent.

Even without new titles, analysts estimated that the Harry Potter series could generate more than £1 million a year in profit for Bloomsbury, although the prices of the books are likely to fall over time.

The final dividend is raised 10 per cent to 3.3p.

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