London is one of the greatest cities on the planet and a large commercial center. It is served by many airports but Heathrow and Gatwick airports are the most famous. There are also other airports such as Luton, Stansted and Southend, which are all located outside the city. Another airport that serves London is London City Airport.
To get from London to Madrid, you will need to note from which airport your plane is taking off. Heathrow Airport is one of the largest and busiest airports in the world. Gatwick Airport has been historically associated with London. Considering the size and stature of London, it is rightly served by six different airports.