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

Return flights

07 Dec - 12 Dec	Icelandair
08 Dec - 12 Dec	Icelandair
10 Dec - 18 Dec	Icelandair
29 Dec - 24 Jan	Icelandair
11 Dec - 16 Dec	Icelandair
11 Dec - 17 Dec	Icelandair
16 Dec - 10 Jan	Icelandair
12 Dec - 16 Dec	Alaska Airlines
10 Dec - 28 Dec	Icelandair
02 Dec - 27 Dec	Icelandair
15 Dec - 27 Dec	Icelandair
19 Dec - 10 Jan	Icelandair
25 Dec - 06 Jan	Air Canada
09 Dec - 20 Dec	Air Canada
26 Dec - 17 Jan	Lufthansa
16 Dec - 08 Jan	Icelandair
17 Dec - 10 Jan	Aer Lingus
22 Dec - 17 Jan	Icelandair
22 Dec - 09 Jan	Icelandair
17 Dec - 07 Jan	Hawaiian Airlines

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.

Book a cheap hotel in London

Cheap car rent in London

Cheapest return flights from Seattle to London in December from 448€

Return flights