Dame Helen Mirren hosts the first episode of this epic TV event series. Over 4 episodes the Houses of Hogwarts will do battle to see which team knows the most about the wizarding world, featuring celebrity guests, actors from the original films and more Harry Potter Magic than you could find on a day trip to Diagon Alley. Tonight's match up sees the brave Gryffindors face the loyal Hufflepuffs for a guaranteed place in the grand final.