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

Return flights

10 Dec - 17 Dec	Icelandair
11 Dec - 17 Dec	Icelandair
11 Dec - 17 Dec	Air France	direct
06 Dec - 07 Dec	Scandinavian Airlines
13 Dec - 03 Jan	Icelandair
30 Dec - 06 Jan	United
30 Dec - 06 Jan	British Airways	direct
15 Dec - 20 Dec	Icelandair
15 Dec - 30 Dec	Icelandair
20 Dec - 10 Jan	Icelandair
18 Dec - 17 Jan	Icelandair
26 Dec - 02 Jan	Air Canada
20 Dec - 27 Dec	United
19 Dec - 28 Dec	United
26 Dec - 02 Jan	Delta	direct
19 Dec - 26 Dec	Air France	direct
21 Dec - 27 Dec	Icelandair
17 Dec - 04 Jan	United
13 Dec - 03 Jan	Air France	direct
20 Dec - 10 Jan	British Airways	direct

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

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 December from 522€

Return flights