Employee working from home full time

t2ange

I am an employee working from home full time as the company does not have external offices. There are three of us employed in this way for approximately 30-35 hours a week. I rent my house and one of my bedrooms is an office for which the company has been paying a proportion of the electricity/water/internet and phone use and rent. I give them evidence of the utilities as I certainly use more than the £3 allowed by HMRC but they are taxing and NI what they pay me for use of the room as it is classed as unearned income, which I understand. The amount involved is far less than if they had to rent office space in a commercial building and they had to my travel expenses to that office. Could anyone please tell me the rules on this as I am not a Director of the company and the contract of employment is for working from a home based office. Can I dictate how much they pay for the use of the room or do they tell me how much they will pay me? Information on this would be really helpful.

Many thanks.