If you want a cheap flight from Mombasa to London, you've got zero airlines to choose from.
Make sure you use the search options above to search for flights to other airports in London, not just London Gatwick. The more options you look at, the better your chance of finding a cheap deal.
You can expect accommodation prices to be higher at this time of year too. Last-minute deals do crop up, but it's best to book everything in advance to avoid disappointment.