HMRC can also collect other outstanding debts through your PAYE tax code this may be of tax credit overpayments or outstanding Class 2 National Insurance.
If this has been the case then the outstanding debt will have been noted on your P2 coding notice, any on your Government Gateway record online.
if an outstanding debt has been included in your tax code then include the amount stated in the notes of your coding notice or through the Government Gateway in this box.