The key thing here is what the loan is used for, not what property it is secured on. For example, where a rental property is (re)mortgaged and the money used to purchase/renovate a PPR the interest would not be allowable against rental income but the owner occupier could claim owner occupier mortgage interest relief (TRS) on it. Or where a PPR is (re)mortgaged and the money used to purchase/renovate a rental property then the interest would be allowable against rental income. Your post does not give enough detail to comment on your specific situation.