Certainly in the UK you should advise the mortgage company of your intentions and most likely they will agree and simply ask for Landlords building insurance and the tenancy is via an assured agreement through an agent. As noted, Buy to let loans often have a higher interest rate and lower loan to value, so they could ask for a chunk of money to align the loan with their products, chances are, for a short deployment they won't . If you just jump ship and put a tenant in, they could, quite legally, get the hump and say you are in breach of contract. It is quite tricky to get a mortgage in UK if your salary is paid abroad and not in GBP,. Best bet, play it straight. You cannot transfer the mortgage to your wife unless she earns enough to support the whole loan amount, and you cannot transfer a mortgaged property unless the mortgage provider agrees.