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

Return flights

07 Sep - 23 Sep	Aer Lingus
14 Sep - 23 Sep	Aer Lingus
07 Sep - 24 Sep	Aer Lingus
03 Sep - 19 Sep	Aer Lingus
10 Sep - 17 Sep	Aer Lingus
02 Sep - 10 Sep	Aer Lingus
01 Sep - 24 Sep	Aer Lingus
01 Sep - 16 Sep	Aer Lingus
02 Sep - 09 Sep	Aer Lingus
02 Sep - 24 Oct	Aer Lingus
21 Sep - 29 Sep	Air Canada
22 Sep - 21 Oct	Aer Lingus
24 Sep - 08 Oct	Air Canada
18 Sep - 09 Oct	TAP
24 Sep - 08 Oct	British Airways	direct
02 Sep - 24 Oct	British Airways	direct
30 Sep - 07 Oct	British Airways	direct
22 Sep - 21 Oct	British Airways	direct
24 Sep - 12 Oct	TAP
30 Sep - 04 Oct	TAP

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 $472

Return flights