Whether or not the interest is deductible depends on the purpose of mortgage. Although the mortgage will be secured on your personal asset, the interest is an allowable deduction when establishing the net profit of the business.
However, you will need to restrict the interest for the original mortgage element, as this is entirely personal.
And furthermore, if any of the re-mortgage funds are to be used for personal reasons, then the interest must be restricted further.
If you would like reassurance that you are claiming all the expenses available to you or you would like to discuss this further, please feel free to contact your local TaxAssist Accountant.