Thank you Jagrup, that is very helpful, especially given the situation is better than I had feared after skimming through the HMRC manual. Obviously I should have spent more time going through the body of text, Apologies, I feel like I've wasted your time.
With regards to your last sentence...
"Alternatively, you are able to purchase your BTL through a limited company first and you will still retain your lower rate of sdlt on the purchase of your main residence if you wish to do it that way round."
This is because HMRC won't look through to the directors and treat any homes in a