Not for Eurostar. Interrail seat reservations are often more expensive than a new ticket.
I've taken Amsterdam-London with Interrail many times, usually €35, sometimes €57, often sold out. So yeah, two price levels; Eurostar is basically SNCF.
alt Hacker News
I've taken Amsterdam-London with Interrail many times, usually €35, sometimes €57, often sold out. So yeah, two price levels; Eurostar is basically SNCF.