We've scanned every flight from Philadelphia to London to find the best deals. If you want a cheap flight, it's best to be as flexible as you can on dates. At the moment, the cheapest flight is on 12 / Feb / 2025. If that day's no good for you, try searching by month to see some alternative dates.
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 Heathrow, it's worth checking your other options. The 5694 km flight usually takes about 9 hrs 40 mins.
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.