British Airways, Iberia, and Finnair have round-trip flights from Austin (AUS) to Glasgow (GLA) for $649 with a connection. Flights September to November. Departures on Monday, Tuesday, Wednesday, and Sunday. 7-day minimum stay required.
Delta, Virgin Atlantic, American, United and partners have flights from Austin (AUS) to Manchester, Glasgow, or Edinburgh (MAN/GLA/EDI) for $553-$561 with a connection. Flights from March to May and also October to December. No Christmas. New Years is available if you can stay 11-days or longer. Flights may operate as a code-share on a Oneworld/SkyTeam/Alliance carrier.
Note: Fare allows for free carry-on bag, but a checked bag will cost +$60 each-way. Upgrades into “Regular Economy” are available for about +$60 each-way. You can avoid paying a seat selection fee by accepting the randomly assigned seat at the gate.