AirHint found the following cheapest return flights from Washington (IAD) to London (LCY) in December 2025 (see full year).

Return flights

03 Dec - 10 Dec	KLM
16 Dec - 09 Jan	SWISS
15 Dec - 23 Dec	KLM
23 Dec - 29 Dec	SWISS
10 Dec - 17 Dec	British Airways
15 Dec - 29 Dec	British Airways
23 Dec - 01 Jan	SWISS
18 Dec - 30 Dec	SWISS
01 Dec - 03 Jan	Aer Lingus
14 Dec - 02 Jan	British Airways
17 Dec - 08 Jan	KLM
28 Dec - 03 Jan	Aer Lingus
22 Dec - 28 Dec	Aer Lingus
23 Dec - 28 Dec	Aer Lingus
19 Dec - 01 Jan	Aer Lingus
19 Dec - 03 Jan	Aer Lingus
20 Dec - 03 Jan	Aer Lingus
18 Dec - 03 Jan	British Airways
03 Dec - 07 Dec	SWISS

Also check the deals for one-way flights from Washington 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 Washington to London in December from $688

Return flights