I have just rented my house out, if the rent covers your mortgage and you are not making any profit you will be ok, we had a statement from our letting agent for tax purposes, but we had paid out more than we had in rent payments since we had to have an energy performance certificate and an electricity check , so did not need to declare anthing in the last tax year because we had not gained any income, you can also offset any cost for repairs and maintenance against any profit made if your rent is more than your mortgage. Hope this helps.