PARIS - LONDON | EUROSTAR train
Several daily connections: rail.cc/en/train/paris-to-london" target="_blank">rail.shop/beurope" target="_blank">rail.cc/en/train/paris-to-london
There is a special passholder fare
for travellers owning a valid InterRail ticket.
The passholder fare is non-refundable
but is exchangeable once before the departure of either leg, subject to seat availability at the time of request.
SINGLE one way: EUR 65 / £57,50 for a single
RETURN: EUR 130 / £100
Where to buy:
You can not buy the ticket to the special InterRail fare online. Often there a special price tickets available beside the Interrail reservation (and much cheaper!): [ux]rail.shop/beurope
Or directly at the Eurostar website.
At a Eurostar Terminal
At the contact centre on 08705 186 186 (in the UK only) or +44 1233 617 575 (international calls).
The ticket to the special passholder fare can not be purchased online!!!
All tickets are sold subject to availability.
All tickets purchased over the phone are subject to a £5 booking fee.
As long as you are in possession of your pass on the day of travel, it is not necessary to validate it first.
CHEAPER normal tickets
(update by SiDUDe):
If you can book in advance you can usually find much cheaper advanced normal tickets, sometimes as low as half the pass holder price for a return, although you have to commit to specific trains on specific days
Avoid the EUROSTAR - use a ferry:
FRANCE (Calais) - UK (Dover)
NETHERLANDS (Hoek van Holland) - UK (Harwich)
Due to the unclear situation of the ferry prices, think about using a bus (also overnight)
IMPORTANT UPDATE: rail.cc/en/train/paris-to-london
Update: Nov 2016