Bradley Blackburn

I am looking to have 2 lodgers in my 3-bedroom property. Because of this, I do not want to use the rent-a-room scheme, as my expenses would be high. As there will be three of us, will I only be able to claim back 66% of the household expenses, such as heating and electricity, on taxes? I assume the mortgage is not an expense I could claim here? Additionally, if I am not able to claim the mortgage as an expense, am I eligible for the Mortgage Interest Tax Relief of 20% of the interest that buy-to-let landlords are eligible for?