Trains from Madrid to London are a scenic way to travel from the capital of Spain to the capital of the UK when you are visiting Europe.
To take a train from Madrid to London, first take a train from Madrid to Paris. You can find out how to do this here.
After you arrive in Paris, you will need to take the Eurostar train from Paris to London. Information on this route can be found here.
Note that trains from Madrid to Paris arrive at Paris Gare d’Austerlitz or Montparnasse station, while trains from Paris to London depart from Paris Gare du Nord station. As such, make sure to leave yourself plenty of time to take the metro, a taxi, or a bus between stations when you arrive.
Also keep in mind that the Eurostar requires you to check in at least 30 minutes prior to departure. Give yourself extra time for the check-in, security, and passport control process, as these can take some time.