Write to the customer services department of the train company you were travelling with. Explain to them what happened, give full details of your journey, and include your tickets (take copies first). Many train companies now provide online forms on their websites to do this. 

In most cases you’ll contact the train company itself (e.g. First Great Western). For journeys on London Underground and London Overground, this will be Transport for London.

For underground services in Merseyside, Tyne and Wear and Glasgow, go to the local Passenger Transport Executive: Merseytravel; Nexus (Tyne and Wear); Strathclyde Passenger Transport (Glasgow) respectively.

If you're not happy with the response you get from the company, or do not receive the refund you think you are entitled to, contact:

• Passenger Focus if your journey was outside London or if your complaint is about the National Rail Enquiries Service
• London Travel Watch if your journey was within London and surrounding areas (including those on London Underground or London Overground).

Explain the situation to them, and include copies of the response you have received from the train company (if appropriate).

If you're unhappy with the response of Passenger Focus or London TravelWatch, get in touch again and raise a complaint with them about how your complaint has been handled.

If you're still unhappy with the way your complaint has been handled, you can take it to the Parliamentary Ombudsman (for Passenger Focus), or the London TravelWatch Chief Executive and, if you are still unhappy with London TravelWatch, the Local Government Ombudsman.