AirHint found the following cheapest return flights from Seattle (SEA) to London (LHR) in September 2026 (see full year).
Return flights
| 23 Sep - 30 Sep | Icelandair | ||
| 02 Sep - 09 Sep | Aer Lingus | ||
| 01 Sep - 08 Sep | Aer Lingus | ||
| 02 Sep - 09 Sep | KLM | direct | |
| 01 Sep - 08 Sep | British Airways | direct | |
| 23 Sep - 30 Sep | Air France | direct |
Also check the deals for one-way flights from Seattle to London in September.
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