How to use Eurostar trains with your Interrail or Eurail pass

If you're travelling Europe by train and plan on visiting the United Kingdom — or perhaps you're starting your journey here — there's a good chance you'll be taking a Eurostar train. The company provides the only passenger rail connection between the UK and the mainland, and serves destinations including London, Brussels, Paris, and Amsterdam.

International Eurostar trains are included with your Interrail or Eurail Global Pass, but there are some extra steps to complete before you can board. The UK is not part of the Schengen Area, so you'll be passing through border control. Plus, as a high-speed, intercity service, you'll need to purchase a seat reservation. But it's straightforward, so don't worry.

Seat reservations

Call it what you like — a seat reservation, supplement, or surcharge — but you will need to pay a bit extra to use Eurostar services. The good news is that this is considerably less than what you would be paying without an Interrail or Eurail pass. It varies slightly with destination and travel class, but is not subject to the same dynamic pricing that full-price tickets are.

However, there are a limited number of seat reservations available to pass holders. They can and do run out, even when there is still space on the train. In which case, you would have to look at booking another train or another mode of transport entirely. You cannot travel on Eurostar trains without a reservation, not even sitting in the vestibules — you wouldn't get through the terminal, let alone board the train.

What to do? Book early, ideally a few weeks (or earlier!), especially at the height of summer. Granted, there are times of year or odd services where you can find a reservation within a week of departure, but you shouldn't rely on it. Although, anything before six months in advance is probably too soon, and reservations may not be on sale yet.

There's not a clear way of knowing how many pass holder reservations are left, other than going to book and seeing whether the train is still available. Speaking of going to book...

Where and how to book

You cannot purchase seat reservations directly from Eurostar, so you'll have to use one of their partner websites. There are a few options.

• RailEurope, which charges no booking fees for Eurostar seat reservations.
• B-Europe, which charges a €4.00 booking fee regardless of the number of passengers.
• Interrail/Eurail, which charges a €2.00 booking fee per passenger.

Select your origin and destination (if you're not too sure, entering the city will give you a 'All stations' option) and desired date and time. Don't forget to add your Interrail or Eurail pass. If you're seeing prices between €35.00 and €43.00, then you've done it right! If it's 'unavailable' or the price is above that range, there's a good chance that pass holder reservations have sold out for that train.

When booking, you might be asked for a 'pass cover number'. If you have a paper pass, enter its number (it should begin with an 'I'). If you have a mobile pass, you'll need to convert your mobile pass reference to a pass cover number. It's really easy, and you can do so on the Interrail or Eurail websites. Importantly, you don't need to activate your mobile pass before booking the seat reservation.

By the way, once you've booked with one of these other websites, you can manage your journey on the Eurostar website. Select 'manage your booking' from the menu and enter your reference (it'll be on the boarding pass shown or emailed to you) and your surname. From here you can change trains (for a fee) or seats (for free) or traveller information.

I booked seat reservations for a trip this summer with RailEurope and had no issues. The tickets were emailed to me immediately after purchase, and I was able to use the Eurostar website to change my seat. Given that they don't charge a booking fee, I'm not sure why someone would prefer to use one of the other options.

Add the journey to your mobile app or write it down on your paper pass, the same way you would for any other train. Congratulations, you'll be taking a Eurostar train — how exciting!

On the day

All that's left is to show up with your belongings and documentation, giving yourself adequate time to pass through security and border control. While this is typically quicker than in an airport, ticket gates still close 30 minutes before scheduled departure. Eurostar recommends that you arrive at the station 75 minutes before departure.

Sit back and enjoy your journey between the UK and mainland Europe.