"If I am off the public highway, am I actually obliged to display my number plates?" - Scott
So I plugged it into Google.
This popped up:
>"Drivers can ride on private land without these requirements [an appropriate licence,
insurance and, where appropriate, a helmet*] as long as they have
permission to be there."
* The document is primarily focused on the use of mini-motos but deals with the requirements of vehicles when used on a public road vs private off-road.
>"Obviously if the attendant cannot see the number plate, then ultimately the authority cannot take any enforcement action. It is, of course, a criminal offence to keep a vehicle on the road without displaying a registration mark. However, parking attendants do not have any powers to enforce criminal law and so if they wish to take the registration mark of a vehicle whose number plate has been obscured, they will need the assistance of the police to remove whatever it is that is obscuring the plate if they are to escape any liability for damage caused. I am instructed that in some cases, particularly in the case of motorbikes, tarpaulins are used to cover the whole vehicle and then a padlock is used to prevent removal. [...] I should make it clear, of course, that the Promoters have no objection to the use of motorcycle covers per se, particularly if the bike is not parked on the highway."
-Source: Paragraph 47 at http://www.parliament.the-stationery-office.co.uk/pa/ld200607/ldselect/ldubcllatfl0506/evid/clla02.htm
Furthermore, (and specific to private parking):
>"...on private land, you don't need number plates.
BUT - private land where the general public is allowed access without having to seek permission, such as car parks are very different. You have to display number plates and you can be fined by the police for motoring offences.
The definition of a road in England and Wales is 'any highway and any other road to which the public has access and includes bridges over which a road passes'. In Scotland, there is a similar definition which is extended to include any way over which the public have a right of passage. It is important to note that references to 'road' therefore generally include footpaths, bridle-ways and cycle tracks and many roadways and driveways on private land (including many car parks). In most cases, the law will apply to them and there may be additional rules for particular paths or ways."
IANAL, but the short answer seems to be: Not advisable, but one option is to create a fake plate which will give rise to nonsensical info by the time they attempt to process the DVLA request and raise a fine - and you'll be on your way.