Four months before its release, the latest instalment in the adventures of Harry Potter is already the fastest-selling book in British history.

Today, the frenzy of anticipation among young old fans alike was cranked up a notch with the publication of the front covers of J K Rowling's Harry Potter and the Half-Blood Prince.

The cover illustration, by Jason Cockcroft, for the children’s edition, which is due to be published on July 16, shows Harry and Professor Dumbledore, the headteacher of Hogwart's wizarding college, surrounded by a circle of flames

Dumbledore has already been tipped as one of the favourites to die in the sixth book after Rowling said one of the lead characters would be killed off.

Brandishing their wands, Harry - whose Quidditch playing appears to have contributed to a muscular adolescent physique - and his bearded headmaster stand in the centre of a ring of magical flame.

Afficiandos of over school-leaving age can preserve a facade of literary respectability by investing in the adult version, more soberly adorned with a photograph by Michael Wildsmith. It shows a battered copy of Advanced Potion Making, suggesting Harry is in line for more bruising lessons from hated potions master Snape.

Rowling has now completed work on The Half-Blood Prince and although the contents of the sixth and penultimate book nre a closely guarded secret.

The author has so far given few clues as to what lies in store for Harry and his pals Ron and Hermione and internet billboards are buzzing with theories.

She has refused to reveal who the Half-Blood Prince of the title is, although she has said it is neither Harry nor his arch-enemy Voldemort.

Although she has assured fans that Harry will definitely survive to the seventh and final book.

The title was originally going to be used for the first book in the meticulously-planned series.

Ms Rowling said: "At the time I quite liked it as the title for the Chamber of Secrets but then I removed a whole storyline and unfortunately it bore no relation whatsoever to the title by the time I'd finished.

"It gave too much information too early, so I pulled it out and it became a major part, but not the only part, of book six.

"There is no trace of that storyline left in Chamber of Secrets. People have been speculating that book six is a spin-off of book two, but it is not."

The book, which is to be printed on ancient-forest friendly paper, has already secured advance sales topping 100,000 and experts at internet store Amazon predict it will outsell the previous instalment - Order of the Phoenix - before it even reaches the shelves.

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