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

Return flights

08 Dec - 14 Dec	Icelandair
02 Dec - 09 Dec	Icelandair
10 Dec - 19 Jan	Icelandair
01 Dec - 10 Dec	Icelandair
05 Dec - 10 Dec	Icelandair
01 Dec - 08 Dec	Icelandair
10 Dec - 10 Jan	Icelandair
03 Dec - 10 Dec	Icelandair
04 Dec - 11 Dec	Icelandair
08 Dec - 15 Dec	Icelandair
29 Dec - 24 Jan	Icelandair
31 Dec - 24 Jan	Icelandair
04 Dec - 17 Dec	Lufthansa
03 Dec - 16 Dec	Icelandair
30 Dec - 19 Jan	British Airways	direct
30 Dec - 24 Jan	British Airways	direct
31 Dec - 24 Jan	British Airways	direct
29 Dec - 10 Jan	Icelandair
11 Dec - 08 Jan	Icelandair
10 Dec - 10 Jan	Air France	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 $479

Return flights