There are zero airlines offering flights to London. The most direct route isn’t necessarily the cheapest – being flexible is key to finding the lowest airfare rates. For example, try searching by month to see the best time of the week to fly.
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 Luton, it's worth checking your other options.
If you're planning on going to London during this time, you could take a look at other airport options. Or you could try to get a last-minute bargain.