Singapore Airlines has round-trip flights from Houston (IAH) to Manchester (MAN) for $576-$639, NONSTOP. Flights September to May. Departures on Tuesday, Wednesday, and Friday. Extended Weekends available.
Note: Some small OTAs on SkyScanner have this for about $556. If you plan on booking there, beware of any site that charges a fee to cancel a ticket within the 24-hour “free” period. Use unknown booking sites at your own risk.