If you have a complaint about Virgin Trains West Coast (i.e. Virgin Trains services that run from Euston rather than Kings Cross) you should do the following steps:
First of all email or write in with your complaint. If you use email make sure you have the word COMPLAINT clearly in the subject line.
PO BOX 713
If you don't receive a response you consider satisfactory within a month please pass to the passenger watchdog Transport Focus.
The form to complain to Transport Focus is here. Please ensure you send them copies of what you've sent Virgin Trains along with any replies you've received. If they have replied please explain why you consider it inadequate.
Also if the complaint is in relation to any misleading advertising, including online, TV, radio or in leaflets or posters please also make the Advertising Standards Authority (ASA) aware and also explain why you find it misleading.