There are 3 local airports in London that are primary hubs for most of the budget-fare U.K. carriers; these are Gatwick, Luton, and Stansted. Several airlines use these airports as their base for London flights.
You can fly with Ryanair, Europe’s largest low-cost airline that offers cheap flights to London; easyJet, also one of Europe’s largest cut-rate carriers, offers cheap London flights as well. Both Ryanair and easyJet offer no-frills budget flights, with unassigned seats, no complimentary food, smaller food portions for meals, and no connecting flights.
Smaller carriers that also offer cheap flights to London through are Jet2.com (based in UK), and airberlin (based in Berlin).
If you prefer more amenities, British Airways, UK’s flag carrier, offers premium economy via World Traveller Plus, which allows subscribers to have the best economy seats, online check-in services, and added baggage allowance; fly with World Traveller Plus and you can earn Tier points and travel mileage points for future discounts and free flights.