Read the following (scroll down to "rail") which gives information when an appeal may be accepted:
http://www.adviceguide.org.uk/index/your_world/travel/public_transport.htmIt deals with disabled passengers.
Read also the relevant posting on Martin Lewis's site:
http://forums.moneysavingexpert.com/showthread.html?t=228562This posting (admittedly from 2006) gives the following information:
You need to phone Revenue Protection Support Services for advice.
P.O. Box 89, Portsmouth, PO1 1EG
Tel: 023 8072 8950
Fax: 023 8072 8904
If you dont get anywhere with them you can appeal against the penalty fare within 21 days of issue to.
Independent Penalty Fares Appeals Service
P.O. Box 14697, London, SE1 8ZJ
Appeals can only be dealt with in writing or online.