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

Return flights

30 Sep - 14 Oct	Icelandair
29 Sep - 03 Oct	Icelandair
29 Sep - 07 Oct	Icelandair
24 Sep - 29 Sep	SWISS
22 Sep - 30 Sep	SWISS
26 Sep - 01 Oct	Frontier Airlines
29 Sep - 04 Oct	Icelandair
27 Sep - 01 Oct	Frontier Airlines
29 Sep - 09 Oct	Frontier Airlines
29 Sep - 02 Oct	Allegiant Air
22 Sep - 29 Sep	Lufthansa
26 Sep - 28 Sep	Frontier Airlines
17 Sep - 24 Sep	SWISS
25 Sep - 01 Oct	Frontier Airlines
28 Sep - 18 Oct	Frontier Airlines
17 Sep - 23 Sep	Air Canada
19 Sep - 26 Sep	Frontier Airlines
22 Sep - 27 Sep	TAP
21 Sep - 28 Sep	SWISS
18 Sep - 26 Sep	Frontier Airlines

Also check the deals for one-way flights from Washington 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 Washington to London in September from 412€

Return flights