The Channel Tunnel Rail Link - also known as High Speed 1 or CTRL - was completed in two phases. The first phase was completed in September 2003, with the second phase fully opened on November 14 2007. It's the first major new railway to be built in the UK in over 100 years and provides a 68 mile high-speed rail link between the UK end of the Channel Tunnel in Kent and St Pancras in London. Since the completion, passengers have been able to enjoy travel times of 2hrs 15 mins to Paris, and 1 Hr 50 Mins to Brussels.

Maximum speed on the line is 300km/hr, although sections through tunnels closer to London are limited to 270km/hr and lower as the trains approach St Pancras, where a superb new international station has been created at St Pancras. This new station acts as an as an interchange between Eurostar, domestic Channel Tunnel Rail Link, Midland Mainline and Thameslink services and several London Underground lines.

Channel Tunnel Rail Link Javelin Train domestic services connect London with Gravesend, Margate and Broadstairs by joining the  network at Ebbsfleet, while services to Canterbury, Ramsgate, and Dover continue to Ashford to join existing routes there.

For more detail on the CTRL, the Wikipedia article has in depth information. Alternatively take a look at the video below for an in depth view of the history of the Channel Tunnel and the rail link through it.

''...high speed Channel Tunnel services linking the UK and Europe...''
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If all of this gets you interested in a trip through the tunnel to France, you may want to ride the High-speed Javelin routes as part of the journey. Timetables for the Javelin service will come in handy too.