The DD mandate is part of the Ulster Bank application form. If an applicant is sale agreed (or switching mortgage) at the time of the application for AIP, then they require the mandate to be completed up front, as Ulster Bank go straight from AIP to loan offer in these cases. If the applicant is not sale agreed, then the DD does not need to be completed until that time.
I wouldn't worry about it either way, though. You gave all of your bank details to the mortgage advisor anyway, and a lot more besides. There's no new information on the DD mandate that would allow anyone to do anything untoward, and the only function of the form is to take mortgage repayments after a mortgage is drawn down.
Best regards,
Dave Curry (broker)
https://www.linkedin.com/in/davecurryirl