As Locations Assistant I helped the Locations team filming in my parents' village, Lacock. They've filmed parts of all the Harry Potter films here, but in this one they actually feature my parents' house as the house Slughorn is staying in (played by Jim Broadbent). In this trailer you can see the house in the first few seconds.
As Harry Potter begins his 6th year at Hogwarts School of Witchcraft and Wizardry, he discovers an old book marked mysteriously "This book is the property of the Half-Blood Prince" and begins to learn more about Lord Voldemort's dark past.