+xHi
You will also see that a "vehicle reg No." is optional, and it says you are to made aware that it can / will be monitored.
Again in the overal picture is the possible issues of not supplying it worth it?
Mobile phone number, email addresses and car registration are ALL optional because otherwise it would infringe the Human Rights provisions
and in most cases are irrelevant to the offence/s.
They'll try to fill in all the blanks on their form and ask you, and then give you a copy which will show "Not obligatory" or Optional (too late).
Know your rights folks and don't give them anything they don't need for their mass intelligence gathering.