If you are booking roundtrip flights to UK from USA then you will be arriving at London’s two main airports – Heathrow Airport (LHR) and Gatwick Airport (LGW). Most flights from the United States arrive at these two airports. If you want to travel to more cities in the United Kingdom then make London as your base and travel to the rest of the country by taking low-cost carriers such as Ryanair and easyJet, both of which offer frequent flights from London to cities such as Birmingham, Bristol, Liverpool and Manchester.