AirHint found the following cheapest return flights from Montreal (YUL) to London (LGW) in September 2025 (see full year).

Return flights

21 Sep - 10 Oct	Air Transat	direct
29 Sep - 10 Oct	Air Transat	direct
29 Sep - 09 Oct	Air Transat	direct
29 Sep - 06 Oct	Air Canada
21 Sep - 11 Oct	Air Transat
24 Sep - 01 Oct	FrenchBee
30 Sep - 07 Oct	Air Transat
22 Sep - 30 Sep	FrenchBee
20 Sep - 11 Oct	Air Transat
17 Sep - 30 Sep	FrenchBee
28 Sep - 08 Oct	FrenchBee
22 Sep - 07 Oct	Air Transat	direct
22 Sep - 24 Sep	Air Transat
17 Sep - 24 Sep	FrenchBee
20 Sep - 24 Sep	Air Transat
20 Sep - 23 Sep	Air Transat	direct
18 Sep - 22 Sep	Air Transat	direct
19 Sep - 30 Sep	FrenchBee
24 Sep - 28 Sep	FrenchBee
19 Sep - 22 Sep	Air Transat

Also check the deals for one-way flights from Montreal 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 Montreal to London in September from 446€

Return flights