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

Return flights

11 Dec - 10 Jan	Icelandair
05 Dec - 12 Dec	Icelandair
08 Dec - 12 Dec	Icelandair
07 Dec - 12 Dec	Icelandair
02 Dec - 09 Dec	Icelandair
04 Dec - 11 Dec	Icelandair
01 Dec - 18 Dec	Virgin Atlantic	direct
05 Dec - 13 Dec	Icelandair
03 Dec - 16 Dec	Lufthansa
02 Dec - 16 Dec	Delta	direct
03 Dec - 16 Dec	Air France	direct
29 Dec - 24 Jan	Icelandair
22 Dec - 09 Jan	Air Canada
11 Dec - 10 Jan	Virgin Atlantic	direct
15 Dec - 10 Jan	Icelandair
24 Dec - 17 Jan	Icelandair
16 Dec - 10 Jan	Icelandair
23 Dec - 17 Jan	Icelandair
26 Dec - 17 Jan	Alaska Airlines
16 Dec - 08 Jan	United

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 418€

Return flights