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

Return flights

29 Sep - 07 Oct	Icelandair
24 Sep - 15 Oct	Delta
22 Sep - 03 Oct	Delta
27 Sep - 18 Oct	Air Canada
28 Sep - 18 Oct	Air Canada
29 Sep - 25 Oct	Air Canada
30 Sep - 25 Oct	Air Canada
21 Sep - 06 Oct	Icelandair
21 Sep - 11 Oct	Virgin Atlantic
26 Sep - 18 Oct	Air Canada
19 Sep - 26 Sep	United
16 Sep - 26 Sep	Air Canada
18 Sep - 27 Sep	Iberia
17 Sep - 23 Sep	Virgin Atlantic
18 Sep - 25 Sep	United
20 Sep - 24 Sep	Frontier Airlines
17 Sep - 23 Sep	British Airways	direct
16 Sep - 26 Sep	British Airways	direct

Also check the deals for one-way flights from Portland 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 Portland to London in September from $504

Return flights