Travelling to Chalet Jordan by train from London is easily done in a day, and makes the travel experience something to be enjoyed, not just endured. It can even be cheaper than the plane in high season.
The closest railway station to Chalet Jordan is Thonon-les-Bains, a 20 minute drive away. There is also a railway station at Cluses, which is closer to Les Gets but also convenient if you are travelling by train to Morzine or Avoriaz.
The quickest route from London is to take the Eurostar from London St Pancras to Paris Gardu Nord, then take the suburban RER to the Gare de Lyon, then a high speed TGV from Paris to Thonon. In the winter season there are normally two direct services from Paris to Thonon on weekends. At other times, you will need to make an easy connection at Bellegarde.
Journey time from London to Thonon can be as little as 7 hours.
A second option is to avoid the cross Paris connection. By taking a Eurostar to Brussels, you can then pick up a direct TGV to Lyon (avoiding Paris) then a regional train to Thonon. This does add an hour or two to the journey time, but makes for a more relaxing journey. You may find you have an hour to kill in Brussels, which is probably a good opportunity to sample their beer and moules frites.
Finally, there is the option of the overnight train from Paris to Cluses. Leaving London on the 7pm service to Paris, you can catch the sleeper train at 11pm from Paris Austerlitz and arrive in Cluses at 8am the next morning.
If you are coming for the skiing, then a big advantage of the trains is that you do not have extortionate additional baggage fees to transport your skis, boots or snowboards.