"The London Underground Customer Charter offers a very straightforward refund system for an individual journey delayed more than 15 minutes (except in circumstances outside LU control such as freak weather or security alerts). Claim forms are available at any London Underground station. The refund amount is the standard single fare for the Underground journey you were undertaking."
The problem is that it's quite a hassle to remember to pick up a form, fill it in, post it back, so now, thanks to Tube Refund with a simple text or email, you get a form created and completed in minutes and you send it off the to London Underground by freepost. Up until the 1st November 2003 the service is free, so make the most of it. After that point it's a fiver for 25 forms and considering you could get from �25 to �92.50 for those claims it's still a bargain.
According to The Times the London Underground only receives 1 refund claim for every 1,600 passengers, so hopefully this service will redress the balance.