Jemma is Dan's wife who often appears in his videos. She also has her own channel although it isn't as famous as Dan's. A friend of their's, Leah, is also a YouTuber. Link below. She appeared in the video HAMSTERS! as a person to race Dan in The Great Hamster Race.
In The Sorcerer's Stone, Harry walks with his white owl, Hedwig, through a snowy cloister courtyard located in Durham Cathedral. Harry first learns to fly a broomstick on the green grass of Hogwarts' school grounds, filmed inside the walls of Alnwick Castle, located 30 miles from Newcastle.
Leavesden is near Pinewood, where they shoot a lot of bond films, infact goldeneye was mostly shot at leavesden. Unfortunately all of the interior shots are sets, not real castle, its cheaper that way, but they are very convincing. I think some of it was filmed in Christ Church college.