There will be better qualified people than me to comment but I would look at the fees involved with 2 mortgages and how much interest you would pay over the lifetime of the mortgage(s). Also if interest rates rise would it be financially better or worse with 2 rising mortgages. An unknown is whether a mortgage company would want to know why you were taking so much equity out and whether they would be ok with that. I don't know how buy to let or second home mortgages differ but I'd be keen to hear other's advice.