Read this: BBC - BBC Internet Blog: What's On BBC Red Button 29th March - 11th April

Summary: Viewers can press red at the start of the programme for the Filthy Cities red button experience with extra filthy footage and fun facts. If you haven't got your cards already they are available for free at your local library from April 1st 2011 while stocks last - please ask at the main enquiry desk. Red button viewers can watch exclusive performances from schools in the semi-final stage. - bbc.co.uk