Hi JC66,
In terms of the selling of a property within the rental business, trading would normally cease when the last property is disposed of, alternatively, if only one property is let out, then when you begin to use the property for non-business purposes, or when the decision was made to not re-let the property as covered in
PIM2510.
If this property was the sole let property within the business, then costs such as council tax, house insurance and electricity bills would not be claimable within the rental business once the tenancy ended.
As for mortgage payments, for the duration that the rental business is trading, you may only claim the interest on the mortgage, not the payment itself at the basic rate as found here:
Restricting finance cost relief for individual landlords.
Thank you.