Allowable expenses can include property rent, mortgage interest and council tax, business rates, water rates, electricity , gas, insurance and security costs. Phone, broadband etc can also be claimed but you must work out the % of business to private use and only claim for business.
With the huge rise in fuel bills, broadband etc rather than claiming the usual flat rate it might be more advantageous to use your bills to work out the actual % of use for your home and claim that way.
So if your home has 5 rooms and one is your home office, workshop or whatever it would mean working out the actual cost for one 5th of your home rather than using the simplified expenses/flat rate method.
In the above example instead of paying £300 pcm for gas/electricity you can claim back £60 of that as a business expense.
Similarly for water rates, council tax, insurance and so on.
When did UK governments lose their way?