Thank you for your question.
To clarify, if you did not claim the £1000 Property Allowance you can claim for the mileage expenses incurred in visiting your properties. Part business and part private - Where the business element and private element can be separately identified, the business element is an allowable deduction.
You must keep clear and complete records in support of any claim you make. Where there is no way to separate the business and private elements, no deduction is allowed. For example, a journey might be for a combined personal and business purposes.
I hope this helps.