Hi,
If you hold a joint bank account then HMRC would expect to see the interest amount split in a 50/50 share based on the level of interest received. Firstly, I would advise to look at
HS300 as this covers non-residents and investment income which may give more in-dept information to your situation.
You may include service charge as a deductible expense if they have been incurred wholly and exclusively for the rental property, found at:
PIM2010 under Box 27 “Legal, Management and other professional fees”.
As mortgage interest is dealt with differently to other expenses, when the interest figure is declared, you will receive relief as a basic rate reduction in Box 44.
Further guidance is attached here:
Restricting finance cost relief for individual landlords
Thankyou.