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

Return flights

03 Sep - 10 Sep	British Airways
24 Sep - 01 Oct	British Airways
30 Sep - 07 Oct	British Airways
09 Sep - 16 Sep	British Airways
20 Sep - 26 Sep	Icelandair
04 Sep - 09 Sep	British Airways
04 Sep - 12 Sep	Delta
07 Sep - 14 Sep	British Airways
08 Sep - 20 Sep	Delta
05 Sep - 12 Sep	British Airways
12 Sep - 15 Sep	Delta
27 Sep - 04 Oct	British Airways
13 Sep - 20 Sep	British Airways

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 467€

Return flights