Find a good deal on your flight from London to Hangzhou with Netflights. If you want to keep your options open, take a look at flights from another airport in London.
Both flight prices and accommodation rates fluctuate throughout the year, but searching by month will reveal the cheapest times to fly.
Or you could broaden your search by looking at flights to other airports in China to see if there are any cheaper options.
Did you know you can also compare hotel and car hire prices in China with Netflights? Take a look to get an idea of prices in Hangzhou.