Julia Abbott

Hi,
We have an annex attached to our house with 2 bedrooms, and self-contained.
a) If we only rented out one of the bedrooms, could it count as 'rent a room' so with the £7,500 tax relief? Or are there no options for this, as the annex is self-contained?
b) Electricity and gas are on the same meter as the main house.
Can we offset electricity and gas usage by the annex guests, deducting the cost from our income?
c) If we can, do we need to estimate the usage of the annex guests?
Thank you.