Change of Name: How can I remove my middle name when the field cannot be left blank?

I have changed my name and am trying to update my details via: https://www.tax.service.gov.uk/digital-forms/form/notification-of-a-change-in-personal-details/ I have changed from a FIRSTNAME MIDDLENAME LASTNAME layout to a FIRSTNAME LASTNAME one. I need to indicate that I have no middle name. The form does not allow me to leave the field blank if I select YES to having changed my middle name. If I select NO, my name will not be changed correctly. Can I enter something akin to NO MIDDLE NAME in the middle name field? Or is the process entirely by machine. If the process does not allow me to remove my middle name, then how can I correctly update my record?

Hi,
 

If the form does not allow you to remove the middle name, please contact our helpline: Income Tax: general enquiries   . Thank you.