It's been a while, but I was here in the UK (I'm australian) with my then British boyfriend (Now my hubby) and we had no problems getting a joint mortgage. I was on an ancestry visa then (had 3years left) - however, it never came up, and wasn't something we were asked about in the process - obviously had to provide passport for ID purposed - but I assume as we both had bank accounts and incomes, it wasn't questioned. (Sounds crazy!)