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

Return flights

22 Sep - 02 Oct	KLM
18 Sep - 22 Sep	KLM
08 Sep - 11 Sep	KLM
22 Sep - 26 Sep	KLM
04 Sep - 08 Sep	KLM
08 Sep - 19 Sep	KLM
18 Sep - 24 Sep	KLM
10 Sep - 17 Sep	KLM
03 Sep - 10 Sep	KLM
25 Sep - 05 Oct	KLM
09 Sep - 26 Sep	British Airways
25 Sep - 28 Sep	KLM
22 Sep - 17 Oct	KLM
24 Sep - 01 Oct	KLM
29 Sep - 02 Oct	KLM
29 Sep - 03 Oct	KLM
28 Sep - 09 Oct	KLM
26 Sep - 03 Oct	British Airways
28 Sep - 10 Oct	KLM
29 Sep - 10 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 $434

Return flights