I agree Martyn, the prices are awful but like Charles I love travelling by train. What I have done on a few occasions was to travel on the cheapest 2nd class ticket from Ashford to Lille, then change onto European trains at much more reasonable prices for 1st class travel. My typical route then was Brussels, Rotterdam, Dusseldorf, Luxembourg, Strasbourg, Freiburg, Basel, Lugano and clearly for that train made much more sense than plane. The change in Lille was a minor inconvenience compared to the savings I’d make travelling Eurostar through to Brussels.
My tickets I’d either purchase through the DB or SBB website and having a half fare card for Switzerland meant I’d get 25% off the non Swiss sectors.
I’ve also found buying tickets this way is much cheaper than buying them in the UK and the SBB will send the tickets to you in the UK.
It’s also worth looking at the Interrail passes.