Opodo pulls up both direct and indirect flight options for London to Haikou (China) side by side. Rank them however suits you, by price or by schedule, and lock in the one that works.
On this route, fares have recently dipped as low as €556. What you end up paying hinges on the specific dates and flight times you select.
Going direct between London and Haikou takes around 16 h and 35 m. Choosing an indirect route will add to that travel time.