Talisman, the snowtrain runs direct from Waterloo Stn in London to Bourg St Maurice on Friday nights and Sat Am throughout the season. It stops at Moutiers, Aime as well as Bourg so you've got access to the Trois Vallees, La Plagen and the Haute Tarentaise. You can stay in Bourg and ski Les Arcs which is a great area in its right and buses run from Bourg to Tignes, Val D'Isere and La Rosiere.
The train does get booked up pretty quickly and it can be noisy, there's usually a disco and bar so don't expect much sleep. The SNCF (French train system) run regular night trains, Service De Nuit from Gare d'Austerliz in Paris to Bourg St Maurice, you just catch the Eurostar from Waterloo direct to Paris Gare de Nord and take a taxi to Gare d'Austerliz. I've used this service and the couchettes are comfortable enough to sleep, don't expect privacy. That said if you time it right you can get an extra two days skiing on your break. Take a look at www.raileurope.com
for more details. The flight advice is good there are lots of special offers at the moment and whilst most flights go to Geneva, Lyon is also a possibility because there is a rail station next to Lyons airport which connects via Chambery to the line to Bourg. The only directs access from Geneva to the Alps is by bus. The geneva airport website give details.
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