The scenario is , a house which has an interest only mortgage with the owners living in the house presently ,if the house is let,can the bank change from interest only?
Some lenders, e.g. National Irish Bank, specify that the loan is a loan for the home, and if it is let out the buy to let rates apply.
They could have something similar for interest only, but it's unlikely. Lenders are more likely to give interest only loans to buy to let properties as the capital can be repaid by the sale of the property.