If you want a cheap flight from Siem Reap to London, you've got zero airlines to choose from.
You can use the filters on your search to see more flights and find cheaper rates – London has more than one airport. So if you don't need to fly into London Stansted, it's worth checking your other options.
During this peak season, hotel and holiday prices often increase too, so it's best to book early. Or you could keep your fingers crossed and hold out for a last-minute deal.