Mortgage interest considered as financial cost

Hi HMRC I remortgage my current living property (House A, currently moregage free) to release the equity to buy a flat (Flat B) to rent out, rather than taking a buy-to-let mortgage on Flat B directly. 1) In this case, can I still claim tax relief from the mortgage interest from House A - as this morgage is solely used to finace Flat B? If it is acceptable, do I need to proof the mortgage from House A is used for Flat B and how can we proof that? 2) is there any limit regarding how much mortgage interest can be claimed - certainly it will be less than the interested paid to lender. As the borrowed money can be over the normal btl mortgage's ltv band 75%. Many thanks Alex

Hi 
As the re-mortgage is against your main residence you cannot claim tax relief on these mortgage payments to set against the property you rent out.
More information about interest relief can be found in our Property Income Manual PIM2050 - Deductions: interest: contents
Thank you.