"If you’re aged 25 or under you can get free tickets to shows across England. Just go to the Arts Council website, enter your postcode and choose a participating theatre, then choose from available free tickets. Then call to book at the theatre’s box office or book online; it’s worth bearing in mind that tickets are allocated on a first come, first served basis. Don’t forget to bring proof of age with you when you pick up your tickets from the box office.
This promotion is part of a pilot scheme run by Arts Council England, running from February 2009 to the end of March 2011, and each theatre has a different number of free tickets available. Although it’s aimed at 16-25s, under 16s can also get free tickets, depending on the show’s age rating." (taken from MoneySavingExpert)