AirHint found the following cheapest return flights from Seoul (GMP) to London (LHR) in September 2025 (see full year).

Return flights

04 Sep - 11 Sep	Air China
04 Sep - 16 Sep	Air China
04 Sep - 07 Sep	Air China
04 Sep - 18 Sep	Air China
04 Sep - 13 Sep	Air China
04 Sep - 15 Sep	Air China
03 Sep - 07 Sep	Air China
04 Sep - 12 Sep	Air China
03 Sep - 30 Sep	Air China
03 Sep - 01 Oct	Air China
10 Sep - 21 Sep	Air China
24 Sep - 01 Oct	Air China
10 Sep - 15 Oct	Air China
16 Sep - 14 Oct	Air China
22 Sep - 01 Oct	Air China
11 Sep - 15 Oct	Air China
17 Sep - 15 Oct	Air China
11 Sep - 16 Oct	Air China
16 Sep - 16 Oct	Air China
21 Sep - 04 Oct	Air China

Also check the deals for one-way flights from Seoul to London 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 Seoul to London in September from $790

Return flights