Vehicle registration plate?

I don't think we'd mention "plate" in this context up north (although it would be understood) - simply (vehicle/car) registration number.

https://www.google.com/search?q=parking+%22ve...

https://www.google.com/search?q=parking+%22ca...

@CM2DD - so would I.

Agree with #3, #4: it's most often a "registration number" or "vehicle registration" in the UK - the gov.uk website seems to use both these terms.

"Car registration number" is also perfectly clear.

"Licence plate number" isn't something we would often say, but everyone would understand it.

This official vehicle tax form* asks for your vehicle registration (number plate).

* But you have to select "no" and then "I have the V5 registration certificate" to see it.

Nur um wieder etwas zu lernen:

Würde "the" gehen ("The user has to enter his licence plate number the registration number")???

The original suggestion (#0) was Please enter licence plate number.

Please enter your registration number is what I'd expect to see in the final BE version of the software.

(Or Enter registration number if it needs to be shorter due to space constraints). 

#15 As it happens, VINs are ubiquitous - British and European cars have them too. Over here, though, no one would associate the phrase "registration number" with the VIN.