In reply to MattJ753:
It depends where in UK you are leaving from (and whether you find Landys comfortable)
We are in London and normally drive to Tignes most years. If you go by tunnel it is about 12 hours door to door and, with fuel, tunnel and tolls costs about £450-500. The French roads are motorway and duel carriageway almost whole way and really easy.
Going by air sounds faster but when you include travel to airport/check-in, baggage pick up and transfer times it is likely to take at least 8 hours or so door to door. Similarly for costs; not just air fare but add in traincar to airport, parking and transfer costs (which are ridiculously high).
For a family of 4 almost certainly cheaper by car. For 2 people, probably cheaper by plane unless you are at peak flying season.
Other benefits of car are ability to take lost of luggage, less hassle and you can save a lot of money by doing a big supermarket shop in Bourg St Maurice.
AS other have pointed out you can get good trains to Bourg from Paris and then catch bus to Tignes. Also there is the ski-train from London to Bourg, either overnight or during the day. Not cheap but very civilised. I have gone by train several times and love it.
If you are going in Jan, which should be low season and you are thinking of driving from, say Yorkshire in a Land Rover? Probably better to fly!
Incidentally, look at flights to Lyon as well. Closer to Tignes and trasnfers may be cheaper. Also worth checking whether car hire will be much more expensive than transfers if there are several of you.