This is the website for the Dead By Dawn Film Festival :
www.deadbydawn.co.uk/main.html
It was on in April of this year, so you'll have to wait until next year, but the site has all the details of all the past festivals.
I usally go to Fright Fest horror film festival in London if I am down there at the time. It's this year from 25th Aug- 29th Aug.
Land of the Dead, A Bittersweet Life!, Do You Like Hitchcock?, Dead Meat, NightWatch(must see film), Day of the Dead 2, Wolf Creek and Born To Fight just to name few playing.
They usually add in a few non horror ones like Bittersweet Life, and Born to Fight.