How Do I Complete a 90-Day Report as a U.K. Citizen When Renewing My Passport?

There is a 21 day window to do a 90 day report, make the report and after you typed in the details, you go and apply for a new passport.

Or you write down your passport details on a piece of paper, store that in a drawer and apply for a new passport. In case your new passport took more then 90 days, you take the paper out of the drawer and use it to fill in the 90 day report.