Train travel within the UK
Most of the time you don't need to travel with ID on UK trains as the traveller’s name are not printed on the tickets. The only time this is not the case is if you have bought a Print-Your-Own ticket , where you will be asked to confirm your ID along with Print-Your-Own tickets. You can use any type of photo ID or a credit or debit card as long as it shows your name.
Train travel on Eurostar
Eurostar requires a valid passport or a valid national identity document (Swiss and EEA citizens) with your photo on it. Babies and children must also have their own valid travel documents.
Train travel across mainland Europe
Carriers require a valid passport or EU identity card (EU citizens) that includes your full name, birthdate, and a photo.