In a few years, there may be direct trains from London to Germany; Deutsche Bahn is
applying to run trains through the Channel Tunnel to St. Pancras. Eurotunnel, who own the tunnel, are apparently keen for them to do so, being considerably in debt and having capacity to spare. There remains a question of safety standards, though, which DB may want amended somewhat:
At present, passenger trains using the tunnel have to be capable of being divided in two in the case of a fire. The safety rules also require operators to use a special locomotive capable of coping with the signals and power supply on both sides of the Channel. Under European Union open access rules for railways, the £5.7 billion High Speed One, due to open in a fortnight between the Channel Tunnel and St Pancras, has been built to accommodate trains from across Europe.
If DB get permission to run services to London, trains could reach Cologne in 4 hours and Frankfurt in under 5. The article doesn't say whether all services would be during daytime hours (as are the current Eurostar services, which, after all, are considerably shorter in duration) or whether there would be overnight sleeper trains from London to the heart of Europe.