Richard Peace has this blow-by-blow description of your options for getting your bike to France by Eurostar.
** Update June 4, 2023 **
Please note – since COVID and Brexit, Eurostar has restricted its bike service. Currently, all bikes need to be bagged or boxed.
Taking bikes on the Eurostar from London to Paris Gare du Nord or to Lille has to be one of the most obvious ways of getting your trusty stead to France. Whilst the train journey itself is wonderfully easy and convenient, there are one or two ins and outs you should be aware of if you want to take your bike on this particular service. If you are aware of the rules in advance, it should all be plain sailing.
A word about folders
First of all a word in support of folders; many cyclists are put off as they think they will be wobbly or inefficient to ride or not able to carry enough of their luggage. But I have used them on the majority of trips to France via Eurostar as they are just so convenient; not only do they make your Eurostar embarking and disembarking so much more hassle-free, they are boon if you plan to be moving around on local transport too (for example, I've taken folders on RER trains around Paris several times and even local buses).
Folders are slightly more twitchy to handle than full-size bikes (though most new folder riders soon adapt and don't notice this characteristic), but are easier to manoeuvre, making them ideal for city traffic. And there are plenty of speedy folders with stiff frames and fast tyres as well as models that can be loaded up for touring.
Be aware that there is a restriction on the size of folding bikes on Eurostar (see the size summary below); Freewheeling France has published several reviews of folders that are small enough to be taken as hand luggage with you on Eurostar. They are Brompton (the most portable of all folders), Birdy, BH Emotion and Tern. I've also taken electric assist versions of the Dahon Curve and Brompton on Eurostar without problems.
Your Eurostar options
Whatever size your bike, you should be able to get it from London to Paris/Lille on Eurostar and vice versa. The longest size measurement is the critical one, so I've broken down the services on offer by size.
1. 85cm or less as hand luggage
This is in fact the limit for all hand luggage you take with you on Eurostar. The folder should be bagged. It's then a matter of taking it through passport and security controls as normal (it will go through the scanner so if it is right on the 85cm limit, take care putting it on the scanner conveyor belt – I know from experience it is possible for your bike to jam on the sides of the machine if you don't feed it in straight...).
If touring around on a folder, it's likely you'll have panniers and/or handlebar and seatpost bags, so using a station trolley is probably a good idea. Trolleys are distributed around St Pancras and Paris Gare du Nord/Lille concourses but aren't always easy to find (though there should be at least one rank of them on the platform when you get off the train). You need a pound or euro coin to unlock them, in the style of supermarket trolleys. You should then be able to relock them on the platform at the other end of your journey.
Once on the train, just look for luggage space as normal; it can help if you board early and/or get a quiet train as there is more likely to be plenty of luggage space. I can't ever recall not being able to find luggage space on the train itself, however, but it's not always been close to my seat.
This is classed as registered luggage and it can go boxed or unboxed. For boxed, you can use your own or send it in the Eurodespatch boxes provided (Eurostar say there is more space for boxed biked than unboxed bikes).
London to Paris:
You should call in advance (UK: 03448 225 822) to reserve a space – I've always found it best to call just before reserving a Eurostar ticket online (have the actual service you want to travel on in front of you on the screen), then once you've bought the ticket, call back immediately with the ticket details to confirm the reservation. It's always worked for me. Note the charges below vary depending on how far ahead you book.
I've always then made sure I arrive at St Pancras International at least an hour and a half in advance to give me time to wheel the bike to the EuroDespatch office (well signed towards the rear of the station complex), before I then check in with the rest of my luggage. Collection/drop off at Paris Gare du Nord is along the walkway at the extreme left of the Eurostar platforms, following signs ‘Bagages Enregistrés Eurostar/Geoparts’. Road access is via rue de Maubeuge.
There is two weeks of free storage, so you can drop you bike off any time in the two weeks leading up to your departure.
Important: You will receive a receipt and you need this for collection on arrival – keep it safe!
London to Lille:
London-Lille-London services differ a little from the Paris services. There are two options: pre-booked and non-pre-booked.
You buy your Eurostar ticket and then contact EuroDespatch to book your bike. We suggest calling EuroDespatch first, confirming bike space availability on your preferred train AND THEN booking your own train seat and calling EuroDespatch straight back to book your bike. That way you know you can get your bike on the same train. You then arrive in plenty of time on the day at St Pancras or Lille to put your bike on a EuroDesptach protective case. It's then placed through X-ray checks and loaded onto the same train as you. With this advanced option there is two weeks of free storage, so you can drop you bike off any time in the two weeks leading up to your departure.
2. Non-pre-booked: You can actually just turn up on the day and ask for your bike to be put on the same Eurostar service you are taking. The risk is that there will be no space. If there is no space, the bike will go on the first available train within a 24-hour period (typically much less than 24 hours). There is an option to leave the bike fully assembled on this service.
The EuroDespatch office in Lille is run through the 'CityOne' office at the Lille Europe station.
3. Over 120cm
If you have an extra long bike it may need to book it on as registered baggage/pre-booked baggage, as above. Boxing required. However note that tandems are specifically prohibited from being carried as registered luggage.
Note maximum weight for services 2 and 3 above is 30kg per item.
Note these bike services are not available for services going to Ashford, Ebbsfleet, Calais, Disneyland Paris, Avignon or Marseille, though a similar service is in operation between London and Brussels.
Where to find EuroDespatch
Paris Gare du Nord contact details
Advance bike booking + bike drop:
Via EuroDespatch: +33 (0)1 55 31 58 33 (Fr)
Follow signs for ‘Bagages Enregistrés Eurostar/Geoparts’
Open 7am-10pm daily
Lille Europe contact details
Advanced bike bookings:
Via EuroDespatch: +33 (0)1 55 31 58 33 (Fr)
Bike drop and on-the-day bike bookings via:
CityOne (EuroDespatch's designated baggage handlers in Lille):
Place de la Gare, 59000 Lille, + 33 (0)3 20 31 23 10
London St Pancras contact details
Advance bike bookings + bike drop:
Via EuroDespatch: 03448 225 822 (UK)
Open 7am-10pm daily
More information on booking bikes on Eurostar:
Richard Peace is well-versed in cross-Channel travel with his various bikes. He is the co-author of the official guidebook to the Avenue Verte, the London to Paris bike path (see his article here for us). He's also the author of Cycling Southern France (UK, US) and Cycling Northern France (UK, US).