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

Return flights

20 Aug - 02 Sep	Aer Lingus
10 Aug - 19 Aug	Aer Lingus
06 Aug - 19 Aug	Aer Lingus
13 Aug - 26 Aug	Aer Lingus
20 Aug - 03 Sep	Aer Lingus
12 Aug - 22 Aug	Virgin Atlantic
04 Aug - 13 Aug	Aer Lingus
12 Aug - 21 Aug	Finnair
04 Aug - 14 Aug	Finnair
20 Aug - 06 Sep	Icelandair
20 Aug - 02 Sep	Virgin Atlantic	direct
27 Aug - 09 Sep	Aer Lingus
06 Aug - 14 Aug	British Airways	direct
13 Aug - 20 Aug	Delta
17 Aug - 21 Aug	Icelandair
20 Aug - 10 Sep	Virgin Atlantic
24 Aug - 02 Sep	Air France
31 Aug - 06 Sep	Icelandair
20 Aug - 08 Sep	Aer Lingus
24 Aug - 02 Sep	British Airways	direct

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 402€

Return flights