Van Seat 61:
Eurostar became a full member of the InterRail & Eurail schemes from January 2017, and InterRail & Eurail passes now cover Eurostar's core routes between London/Ebbsfleet/Ashford & Paris/Brussels/Calais/Lille/Disneyland. It will also cover the UK-Amsterdam route when this starts. However, the direct Eurostar between the UK & Lyon/Avignon/Marseille and the Eurostar ski trains to/from the French Alps are not covered.
To travel on Eurostar with an InterRail or Eurail pass you must pay a special passholder fare, €30 in standard class if you have a 2nd class pass or €38 in standard premier if you have a 1st class pass.
Passholder places are controlled by a quota but you'll find plenty of availability if you book in advance and (I'm told) you should find reasonable availability even on the day of travel. Just bear in mind that the passholder quota may be set to zero on the busiest trains at peak times, for example Friday & Sunday afternoons & evenings are particularly busy.
If you have a flexi-type pass, yes, using a Eurostar passholder fare requires you to use one of your unlimited travel days, though of course you can use other trains that day in addition to the Eurostar in the countries for which the pass is valid.
To qualify for these passholder fares your pass needs to cover either the country where your Eurostar journey starts, or the country where it finishes, or both. So even a pass which just covers France will allow you to buy a cheap passholder fare between London & Paris. Similarly, even if all you have is a Benelux pass, this allows you to buy a Eurostar passholder fare between London & Brussels. A very attractive deal!
Dit is een flinke verbetering, want eerder kon het enkel met de peperdure tickets voor € 75, waardoor het vaak goedkoper was om tijdig een los ticket te boeken.
Meer informatie: http://seat61.com/London-to-Paris-by-tr ... assholders