The English Channel is the only piece of water in Europe where the train is the dominant cross-border transport — entirely because of the Tunnel and Eurostar. For travellers comparing options, the choice between Eurostar, flying, and ferry is unlike any other in Europe.
Eurostar London ↔ Paris/Brussels/Amsterdam. Total door-to-door time is 3.5-4.5 hours from city centre to city centre. Tickets from £39 advance, typically £79-130 closer to travel, £200+ walk-up. Smooth check-in (30 minutes pre-departure, not 90), full-size luggage, no liquid restrictions, plug sockets and a quiet car. This is the obvious winner for most leisure and business trips.
Flying London ↔ Paris/Amsterdam/Brussels. Around 1.5 hours in the air. But Stansted/Luton + airport transfer + 90-min check-in + arrival immigration + transfer to city centre = 4-5 hours door-to-door, often more. Tickets €30-150. Realistically only worth it if you're flying to/from a non-Eurostar destination on the same day, or if you're connecting onward beyond Paris/Brussels/Amsterdam.
Ferry Dover ↔ Calais (P&O, DFDS). 90 minutes water crossing, but London-Dover or Calais-Paris transfers add 4-6 hours total. £30-80 foot passenger, much more if you're taking a car. Almost never the right choice for foot passengers unless you specifically want the experience. With a car: still relevant — Eurotunnel Le Shuttle is the faster car-train alternative.
The Tunnel: car. Eurotunnel Le Shuttle (drive your car onto the train) crosses in 35 minutes. From £49 one-way advance, more typical £80-160. Total door-to-door London-Paris is about 6 hours if you drive both sides. Useful if you need the car at the destination or have heavy/oversized luggage.
Connecting onwards. Eurostar's strength: from Paris/Brussels/Amsterdam you connect into the high-speed network for Cologne, Frankfurt, Berlin, Lyon, Marseille, Geneva, Zurich. From the airports you connect into the airline network — different destinations win.
Climate: Eurostar saves roughly 90% of CO₂ vs flying for the same trip — about 6 kg vs ~70 kg per passenger London-Paris. Currently the most-significant single climate decision a London-Europe traveller makes.
If your trip is into Western Europe (France/Belgium/Netherlands/Germany) and you don't need a car at the destination: take Eurostar. If you're connecting onward to Spain, Italy or Eastern Europe and want to avoid an extra transfer day: fly. If you need your car: Eurotunnel Le Shuttle.