Swiss Valais and Oberland via Swiss train service

To travel to the Valais by train, there are at least two good options:

• London to Paris by Eurostar, and then onwards to Lausanne, to connect with the Swiss IR trains. This is well described by the Man in Seat 61.
• Eurostar and TGV Lyria offer a service from London to Brig, via Lille (avoiding the Paris station change). This is a great way to travel to Arolla or Zermatt, but unfortunately it only runs on selected Saturdays in winter.

Alternatively, you may just want to consider taking the train to Geneva, to take a Swiss rail link or a resort transfer service.

The Man in Seat 61 says:

Taking the train is the scenic, stress-free and environmentally-sound way from London to Geneva.  Eurostar links London and Paris in just 2 hours 20 minutes from £69 return.  High speed TGV Lyria trains then link Paris with Geneva in just over 3 hours from £23 each way in 2nd class or £62 in 1st class.  ...  Sit back with a glass of wine and enjoy the scenic stress-free alternative to flying to Geneva.