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

Return flights

21 Sep - 12 Oct	Brussels Airlines
28 Sep - 11 Oct	Brussels Airlines
27 Sep - 30 Sep	Austrian Airlines
30 Sep - 08 Oct	Brussels Airlines
21 Sep - 20 Oct	Air Serbia
21 Sep - 24 Sep	Brussels Airlines
23 Sep - 25 Sep	Brussels Airlines
14 Sep - 20 Sep	Air Serbia
25 Sep - 10 Oct	Brussels Airlines
23 Sep - 08 Oct	Brussels Airlines
26 Sep - 30 Sep	SWISS
28 Sep - 04 Oct	Air Serbia
26 Sep - 03 Oct	SWISS
02 Sep - 22 Oct	Lufthansa
24 Sep - 30 Sep	SWISS
12 Sep - 17 Sep	SWISS
15 Sep - 18 Sep	SWISS
16 Sep - 18 Sep	SWISS
12 Sep - 18 Sep	SWISS
23 Sep - 20 Oct	SWISS

Also check the deals for one-way flights from London to Sofia 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 Sofia in September from 143€

Return flights