I think this could be a how long is a piece of string? question as would entirely depend on the rate that someone was on. You need to take into account the fact that most buy to let mortgages will require a minimum 75% deposit and there are lots which require 60% so you will be cutting it fine if you want to borrow £150k against a value of £210k. Have you thought of selling the property with the tenant in situ?
Mine is £280 for about £86k ltb but that's interest only and 80% ltv. For various reasons we couldn't get the best deals. It really does depend on so many things. My 140k residential fixed rate is £680 again I think at about 80%
Interesting, thanks guys. We don't want to sell yet but maybe next year. We might be able to get away with borrowing 100k. I can't quite believe we're in this situation having been mortgage free for years but house prices here have shot up and to buy a family home we need more money.