It’s going to boil down to SRT. If you work outside the U.K. full time then you’re a none U.K. resident from day one. As you’re under PAYE, even though outside the U.K., I’d suspect HMRC will fully tax you and so will the IRS. You’d use FTC against your IRS liability though. Best to get on to US payroll from day one, as you’d want the all important medical. If you can do this, it’ll make it easier to register as a none resident landlord.