AirHint found the following cheapest return flights from Philadelphia (PHL) to London (LGW) in September 2025 (see full year).

Return flights

10 Sep - 15 Sep	Frontier Airlines
07 Sep - 17 Sep	Spirit Airlines
10 Sep - 19 Sep	Frontier Airlines
06 Sep - 14 Sep	Spirit Airlines
10 Sep - 14 Sep	Frontier Airlines
07 Sep - 13 Sep	Frontier Airlines
17 Sep - 20 Sep	Frontier Airlines
18 Sep - 20 Sep	Frontier Airlines
17 Sep - 21 Sep	jetBlue
18 Sep - 21 Sep	jetBlue

Also check the deals for one-way flights from Philadelphia to London in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Philadelphia to London in September from 436€

Return flights