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

Return flights

15 Sep - 23 Sep	Lufthansa
18 Sep - 25 Sep	KLM
18 Sep - 24 Sep	KLM
24 Sep - 29 Sep	KLM
22 Sep - 25 Sep	KLM
23 Sep - 03 Oct	KLM
18 Sep - 22 Sep	KLM
24 Sep - 01 Oct	KLM
11 Sep - 18 Sep	KLM
18 Sep - 29 Sep	KLM
22 Sep - 10 Oct	KLM
19 Sep - 30 Sep	Lufthansa
19 Sep - 23 Sep	Lufthansa
24 Sep - 02 Oct	KLM
25 Sep - 08 Oct	KLM
22 Sep - 02 Oct	KLM
28 Sep - 03 Oct	KLM
28 Sep - 02 Oct	KLM
25 Sep - 06 Oct	KLM
17 Sep - 21 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 281€

Return flights