Screwing means you can stick them both together, back to back, and then drive with the off road version and then when stopped, say you had been to a show or a photoshoot and had forgot to turn them over, get your little electric screwdriver out and flip them over.
Just for anyone that is looking to get show plates or plates with "off road" spacing, it will be illegal for plate companys to produce these plates after October the 1st and they will be subject to a £2K fine if they do so. An interesting fact of this is that no garages will be able to add their phone numbers etc to the the plates!