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Young Person's Railcard http://www.16-25railcard.co.uk/
Bus
If there is a town that you can't get to by train, you will probably be able to get there by coach. You can also take a coach right to the center of London (Victoria Station). National Express is the major provider of coach services; you can find time tables and fares on their website or at their office near the bus station on Drummer Street. Consider buying a Student Coachcard (called an NX2 card), which will save you up to 30% on ticket purchases. If you're up for the longer bus rides (instead of trains), MegaBus can save you bundles on traveling within Great Britain (www.megabus.com).
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