Not an expert or an adviser, but 2 penneth.
Could you raise a residential mortgage on the property you are about to buy, you currently do not have a residential mortgage and you have a substantial deposit, it could be a second home or holiday home etc. Then when you have completed the renovation, you could ask for a consent to let from the lender. Now what normally happens is that when you receive a consent to let the lender increases the interest premium, but if you take out a mortgage with no tie ins say on just SVR you call always switch to a proper buy to let mortgage. I know a friend that did receive a consent to let on his property becasue he was moving jobs, and the lender didn't increase the interest premium at all, or so he told me, it was with Cheltnham and Gloucester.
You would have to pay tax on letting income and capital gains when the property was sold as you will know, but I can't see how your tax situation would be affected otherwise.