The Harry Potter books have proved highly lucrative for Bloomsbury

Bloomsbury's shares sank 30% after it said lower-than-expected pre-Christmas sales and delays in selling rights to reference books could hit profits.

Annual profits for 2006 are set to be only �5m, against predictions of �20m.

Bloomsbury posted profits of �4.2m for the first half of the year, helped by sales of the paperback edition of Harry Potter and the Half-Blood Prince.

Its best-selling titles in recent months have included My Take by Take That member Gary Barlow, Schott's Original Miscellany and Al Gore's An Inconvenient Truth.

Beyond Potter

In a statement issued late on Monday, Bloomsbury said it remained "confident of a satisfactory outcome for 2007".

It also said that if it completed the planned reference rights sales, and if retail sales increased, its annual profit would be close to analysts' predictions.

Despite these comments, shares in Bloomsbury were trading down 91 pence, or 29%, at 219p in lunchtime trade.

The stunning global success of the Harry Potter books has generated bumper profits for Bloomsbury and analysts have been looking to see whether the firm can diversify successfully as the Potter series draws to a close.

Bloomsbury has not yet unveiled when the seventh and final book in the Harry Potter series will be published.