Eurostar - London to Provence - May 2015

That will be quite convenient for you, I would think? (Assuming you can travel in the other direction!)

I would think a lot of British people would be interested in escaping the fog and dreariness for a cheap holiday like that.

Well, yes and no. The nearest train station for departures is either Marseilles or Avignon and I live near Aix. This would entail further costs and having to catch another train or bus.
Anyway, it certainly is worth the ride if the fares are cheaper than airline tickets. EJ prices are ridiculous and they are even charging for seat reservations.