Ant and Dec were also at the star-packed awards ceremony, and were the first people to stand and applaud Cat as she was given the prize by Pop Idol judge Simon Cowell.
Animated movie Shrek took home the best Film Award, beating off competition from The Grinch and Spy Kids.
Special prize for Grange Hill
Grange Hill won a special award for outstanding creative contribution at the bash in London.
Also in the audience were Olympic Gold medallist Denise Lewis, boxer Audley Harrison, Saturday Show presenter Dani Behr, and EastEnders actor Todd Carty, who plays Mark Fowler, and used to star in Grange Hill.