Relief for interest on existing joint mortgage

A deed of trust has been completed allocating rental income 99% to wife and 1% to husband who is a higher rate taxpayer. The property was formerly PPR purchased with a joint mortgage which is still outstanding. How is the mortgage interest allowed against the rental income? Is it 50% each or shared 99%/1% or something else? Thank you

Hi,
Please ref to our guidance using the link below:
UK property notes (2022)
Thankyou.