If you want a cheap flight from Dominica 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.
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.