The Eurostar web site allows you to book to/from any station in the UK from/to major stations in France (including Perpignan), Germany and Benelux - I did this last year and got tickets from High Wycombe-Strasbourg. Of course the Eurostar segment is still an order of magnitude more expensive than continental travel (maybe part of that is the chunnel fee, we'll have to see what happens if DB start through trains), and the Wycombe-London segment cost almost as much as Paris-Strasbourg
London-Strasbourg takes only 4.5 hours, which must be competitive with flying, though it does involve a 500m stroll from Gare du Nord to Gare de l'Est.