"Also car drivers can be identified by their registration"

No they cannot." I would not wish to be too categorical on that point.

I refer you to my earlier post:
From: Iains - PM
Date: 04 Jan 18 - 06:13 PM

Perhaps you think the security services as as daft as you are? Should you be a person of interest rest assured you will not proceed unless they are satisfied that they know who you are. Being complacent on account of not having been stopped before does not change the requirement to have adequate ID
If you take a car not belonging to you on a ferry a sensible precaution would be to have a letter of authorization, should you be stopped. This could also extend to company cars. It would rather depend upon what reasons triggered your being of interest. For certain european countries the registration document is required to be in the vehicle at all times, as is the requirement to carry your driving license in Ireland.(road traffic act 1994 section 40.1 a)

You can be as cute as you like with me. I do not recommend the same line of backchat with the authorities on the day you become one of those "selected" for a little chat. Uniforms do not warm to "clever" people.