AirHint found the following cheapest return flights from London (LCY) to Keflavik (KEF) in September 2025 (see full year).

Return flights

24 Sep - 30 Sep	Lufthansa
01 Sep - 30 Sep	SWISS
10 Sep - 15 Sep	Lufthansa
17 Sep - 06 Oct	KLM
25 Sep - 02 Oct	KLM
25 Sep - 01 Oct	KLM
17 Sep - 22 Sep	KLM
04 Sep - 14 Sep	KLM
24 Sep - 01 Oct	KLM
25 Sep - 29 Sep	KLM
04 Sep - 08 Sep	KLM
18 Sep - 24 Sep	KLM
18 Sep - 22 Sep	KLM
25 Sep - 28 Sep	KLM
25 Sep - 03 Oct	KLM
24 Sep - 12 Oct	KLM
29 Sep - 06 Oct	KLM
29 Sep - 05 Oct	KLM
28 Sep - 05 Oct	KLM
29 Sep - 03 Oct	KLM

Also check the deals for one-way flights from London to Keflavik in September.

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 London to Keflavik in September from 254€

Return flights