Had to attempt to get an expat mortgage 18months ago for a let property i own with by brother. I am UK, but he is in Germany, so we needed to look at ex-pat mortgages.
Probably best to use a broker for these, i used John Charcol who seemed good, but be prepared for high rates & fees for an expat mortgage.
Best rate we were offered at the time was 4.15% with £1500 in fees, because of that we bailed on the idea, did some equity transfer jiggery pockery getting the property in my sole name, then got a standard BTL mortgage at a much more appealing 2.35% with 1/3 of the fees too.