AirHint found the following cheapest return flights from Seattle (SEA) to London (LTN) in August 2025 (see full year).

Return flights

17 Aug - 03 Sep	Aer Lingus
26 Aug - 02 Sep	Icelandair
21 Aug - 28 Aug	Aer Lingus
20 Aug - 27 Aug	Condor
18 Aug - 02 Sep	SWISS
20 Aug - 25 Aug	Condor
22 Aug - 02 Sep	Icelandair
31 Aug - 20 Sep	Icelandair
25 Aug - 18 Sep	Aer Lingus
25 Aug - 02 Sep	Icelandair
17 Aug - 04 Sep	Aer Lingus
21 Aug - 27 Aug	Icelandair
24 Aug - 30 Aug	Icelandair
19 Aug - 24 Aug	KLM
18 Aug - 13 Sep	Icelandair
25 Aug - 31 Aug	Icelandair
19 Aug - 13 Sep	Icelandair
20 Aug - 31 Aug	Icelandair
21 Aug - 26 Aug	Aer Lingus
18 Aug - 29 Aug	SWISS

Also check the deals for one-way flights from Seattle to London in August.

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 Seattle to London in August from 680€

Return flights