England is served by two main airports, Heathrow and Gatwick. Heathrow is one of the busiest airports in the world and is well connected for London. Gatwick is a bit further away from the capital and smaller. When I used to travel for work, I would always see if I could fly from here. It’s often cheaper to go in and out of Gatwick and frequently doesn’t make much difference to your connection time. It’s a bit more manageable –with smaller queues– as well.
If you’re flying from Europe, flights to and from Stanstead are often cheaper. It is quite far from London itself though.
Getting from the airport
Public transport in the UK is often expensive and can be frustratingly unreliable, but it isn’t usually dangerous, so there is no particular reason to avoid it for safety reasons. You can plan train journeys and buy tickets in advance from National Rail.
Unless you’ve got cash to spray around, I don’t recommend booking a taxi from the airport arrivals area. Ride-sharing apps like Uber work, but don’t overlook booking a limousine service from somewhere local to the place you are going. There’ll be someone there to meet you waving a card with your name on it, like you are in a swanky film or something, and this can often be a lot cheaper than you would imagine.