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You can take a Eurostar to Lille, stop over and then catch TGV to the Alps in the morning, with some TGVs are direct to the Tarentaise and others via Lyon.
Stopping over a night in Brussels on your outbound journey opens up more travel options, and means you'll arrive in resort earlier the next day.
Eurostar's direct service from London to Lyon opens up some exciting new journey prospects for skiers - but sadly looks unlikely for winter 2018-19.
If your accommodation is Sunday - Sunday, you can use the new direct Eurostar London-Lyon service to create a stopover journey to the Alps, arriving in resort before those who fly and skiing the Sunday you arrive. Nice.
Think you need to travel to the Alps straight through in one go? Think again! By stopping over a night in Paris, you can catch a wider range of TGV trains the next morning.