JK Rowling recently joined Forbes magazine's list of billionaires

The epic adventure took the award ahead of novels from Ian Rankin, James Herbert, Mark Haddon and Colum McCann.

Some 148,000 readers cast votes via book stores, the internet and libraries to select winners in eight categories.

Rowling, who recently joined Forbes magazine's list of billionaires, described the award as "wonderful".

Unabashed

"Unabashed adult Harry Potter fans are very dear to my heart, and obviously in the case of The Order Of The Phoenix they were the ones who were physically able to lift the book," she added.

Monica Ali's Brick Lane was among the other award winners

Other winners icluded Monica Ali, whose Brick Lane won the debut novel award, and Terry Pratchett - who took the teen choice award with The Wee Free Men.

Michael Moore's Dude, Where's My Country? scooped the factual award, while the autobiography and biography award was won by Nigel Slater's Toast.

The lifesyle award went to The Million Pound Property Experiment by Colin McAllister and Justin Ryan, and the travel writing prize was won by Geoff Dyer's Yoga For People Who Can't Be Bothered To Do It.

Go: An Airline Adenture by Barbara Cassani and Kenny Kemp, took the business award.

The literary award, decided by a panel of judges rather than public vote, went to US writer Richard Powers for The Time Of Our Singing.