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

Return flights

24 Sep - 15 Oct	Icelandair
22 Sep - 06 Oct	Icelandair
28 Sep - 13 Oct	Icelandair
29 Sep - 09 Oct	Icelandair
22 Sep - 03 Oct	Icelandair
11 Sep - 18 Sep	Icelandair
08 Sep - 22 Sep	Icelandair
11 Sep - 16 Sep	Icelandair
01 Sep - 30 Sep	Air Canada
02 Sep - 11 Sep	Air Canada
02 Sep - 09 Sep	United
23 Sep - 30 Sep	United
01 Sep - 15 Sep	Air Canada
17 Sep - 24 Sep	Icelandair
08 Sep - 20 Sep	Air Canada
29 Sep - 09 Oct	British Airways	direct
26 Sep - 03 Oct	United
29 Sep - 06 Oct	United
28 Sep - 13 Oct	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 $503

Return flights