According to This is Gloucestershire, Harry Potter and the Half-Blood Prince is going to return to Gloucester, where scenes from both Harry Potter and the Sorcerer's Stone and Harry Potter and the Chamber of Secrets were shot.

They stated:

Filming will take place at Gloucester Cathedral, with pupils from several local schools tipped to appear as extras in the multi million-pound production...{@@@newline@@@}{@@@newline@@@}Now pupils from King's, Crypt and Denmark Road High School for Girls have the opportunity to audition for roles in the film...{@@@newline@@@}{@@@newline@@@}The cloisters at the Cathedral double up as areas in the Hogwarts School of Witchcraft and Wizardry, where Harry and friends Ron and Hermione, live out many of their fantastic adventures.

Harry Potter and the Half-Blood Prince opens November 21st, 2008.