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

Return flights

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

Book a cheap hotel in London

Cheap car rent in London

Cheapest return flights from Washington to London in September from $490

Return flights