My numbers (in post #1) are correct, my tax liabilities and yields are also understood and correct.
I fully understand the risks involved, and (the information I was particularly looking for) I now know the reasoning behind the banks' apparent reluctance to release equity from a PPR.
.
The figures in post 1 don't allow for the fact that the mortgage interest of 75% will be based on both loans. What makes up your annual 7.5K cost and where are you getting the rental figure from. I know rents are extraordinary currently, but eventually they will start building.
What risks do you understand.