https://www.gov.uk/guidance/income-tax-when-you-rent-out-a-property-working-out-your-rental-income
Allowable expenses
When you work out your taxable rental profit you can deduct allowable expenses from your rental income. The expenses must be wholly and exclusively for the purposes of renting out the property. This means that if an expense wasn’t incurred for the purpose of your property rental you can’t offset the cost against the rental income.
An example of expenses incurred wholly and exclusively for the property rental business. The expenses must also be revenue, rather than capital expenses (explained further below). Common types of expenses you can deduct if you pay for them yourself are:
general maintenance and repairs to the property, but not improvements (such as replacing a laminate kitchen worktop with a granite worktop)
water rates, council tax, gas and electricity
insurance – landlords’ policies for buildings, contents and public liability
interest on a mortgage to buy the property (see below for more information)
costs of services, including the wages of gardeners and cleaners
letting agent fees and management fees
legal fees for lets of a year or less, or for renewing a lease for less than 50 years
accountant’s fees
rents (if you’re sub-letting), ground rents and service charges
direct costs such as phone calls, stationery and advertising for new tenants
vehicle running costs (only the proportion used for your rental business)
Expenses you can’t claim a deduction for include:
the full amount of your mortgage payment – only the interest element of your mortgage payment can be offset against your income. See below for more information
private telephone calls – you can only claim for the cost of calls relating to your property rental business
clothing – for example if you bought a suit to wear to a meeting relating to your property rental business, you can’t claim for the cost as wearing the suit is partly for your rental business and partly to keep you warm and decent – no identifiable part is for your property rental business
personal expenses – you can’t claim for any expense that was not incurred solely for your property rental business
Claiming part expenses
You might incur a cost where only part of it is expense for your property rental business. If a definite part of a cost is expense incurred wholly and exclusively for the property business, you can deduct that part. For example, if a property is used for private purposes for 3 months and commercially let for 9 months, then 9/12ths of the mortgage interest can be deducted from the rental income.