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

Return flights

10 Aug - 27 Aug	Aer Lingus
25 Aug - 03 Sep	Aer Lingus
06 Aug - 09 Sep	Aer Lingus
06 Aug - 11 Sep	Aer Lingus
06 Aug - 27 Aug	Aer Lingus
11 Aug - 27 Aug	Aer Lingus
20 Aug - 27 Aug	Delta
11 Aug - 02 Sep	Air France
12 Aug - 02 Sep	KLM
19 Aug - 04 Sep	Air France
20 Aug - 10 Sep	Virgin Atlantic
19 Aug - 29 Aug	Air France
12 Aug - 27 Aug	Delta
20 Aug - 03 Sep	Delta
11 Aug - 20 Aug	Air France
12 Aug - 20 Aug	Delta
20 Aug - 26 Aug	Delta
06 Aug - 27 Aug	British Airways	direct
19 Aug - 04 Sep	British Airways	direct
11 Aug - 02 Sep	Virgin Atlantic	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 $473

Return flights