LONDON: Harry Potter is continuing to work his magic for publisher Bloomsbury 20 years after his debut, with special editions of his first adventure helping revenue rise 15 percent.

Bloomsbury released new editions of J.K. Rowling's "Harry Potter and the Philosopher's Stone" with covers dedicated to wizarding school Hogwarts' houses Gryffindor, Slytherin, Hufflepuff and Ravenclaw to mark the anniversary in June.

The new designs helped Bloombury's children's trade division deliver what it said was "another outstanding" performance, increasing revenue by a third in its first half.

Revenue from Harry Potter grew 40 percent in the period, the company said on Tuesday, and the young wizard and his magical world will feature strongly in the publisher's assault on the important Christmas market.

"We have a strong second-half list including the illustrated edition of 'Harry Potter and the Prisoner of Azkaban,' the illustrated edition of 'Fantastic Beasts and Where to Find Them' and two major books to accompany the British Library's Harry Potter exhibition," said Chief Executive Nigel Newton.

The robust performance from Bloomsbury reflects a wider improvement in the British book market, where special editions featuring vintage covers and new artwork have helped draw readers back to print formats.

Print revenue was more than nine times as big as e-book revenue, the company said, with the rate of growth identical for both at 16 percent.

The company, which also published 2017 Man Booker prize-winner George Saunders' "Lincoln in the Bardo", reported revenue of 72.1 million pounds ($95 million) and adjusted pretax profit of 2.5 million pounds in the six months to end-August, up 74 percent.

Shares in the group were trading up 4 percent at 167 pence at 0836 GMT.

Analyst Steve Liechti at Investec said Bloomsbury's second-half list looked strong, with cookery titles from Paul Hollywood, Tom Kerridge and Hugh Fearnley-Whittingstall as well as the new Harry Potter editions.

He has a "buy" rating on the stock and a pretax profit forecast of 12 million pounds for the full year.—Reuters