You’ll need to find a reasonable method of dividing your costs, for example by the number of rooms you use for business or the amount of time you spend working from home.
Example
You have 4 rooms in your home, one of which you use only as an office.
Your electricity bill for the year is £400. Assuming all the rooms in your home use equal amounts of electricity, you can claim £100 as allowable expenses (£400 divided by 4).
If you worked only one day a week from home, you could claim £14.29 as allowable expenses (£100 divided by 7).