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

Return flights

04 Dec - 29 Jan	Icelandair
09 Dec - 11 Jan	Icelandair
06 Dec - 14 Dec	Icelandair
03 Dec - 09 Dec	Icelandair
02 Dec - 09 Dec	Icelandair
03 Dec - 10 Dec	Icelandair
01 Dec - 08 Dec	Icelandair
03 Dec - 16 Dec	Icelandair
02 Dec - 08 Dec	Icelandair
03 Dec - 08 Dec	Icelandair
11 Dec - 11 Jan	Icelandair
03 Dec - 11 Dec	Virgin Atlantic	direct
02 Dec - 09 Dec	British Airways	direct
31 Dec - 18 Jan	Delta
09 Dec - 11 Jan	Delta	direct
31 Dec - 18 Jan	British Airways	direct
04 Dec - 29 Jan	British Airways	direct
12 Dec - 11 Jan	Air France
16 Dec - 12 Jan	Air Canada
28 Dec - 17 Jan	Air France

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 411€

Return flights