If you want a cheap flight from Pisa 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 Gatwick, 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.