Hi Kliment Paskalev,
Mortgage interest payments are treated as a deductible when computing profits in respect of a Furnished Holiday Let .
The finance costs and interest restrictions set out in PIM 20250 onwards do not apply to loans taken out in respect of FHL's.
To qualify as a holiday let , the property must meet the availability condition ie, your property must be available for letting as furnished holiday accomodation letting for at least 210 days in the year.
From your comments it does not appear to meet this condition .
HS253 Furnished holiday lettings (2020)
sets out the conditions for FHL