The situation seems to work like this. Buy an old banger in a European Country (usually Germany but not exclusively so) drive it into the UK, and then drive around with impunity safe in the knowledge that you have immunity to any Gatso offences or Congestion Zone charges and are completely exempt vehicle tax (are you reading this Gordon). If you fancy some free petrol, no problem simply fill up and drive out. Take a look at the millions owed to Transport for London in unpaid Congestion Zone charges by foreign plated vehicles. Well guess what most are not foreign they now live in the UK but have never been registered. Once the car acquires too many Police PNC interest reports dump it on a local council estate, take an Easyjet flight to Europe and buy another. Its hilarious how many gentlemen you see of West African origin (this is not just a European problem, oh no) driving around in German plated bangers.
The Police will often avoid this problem due to the hassle of language and the sheer administrative difficulty of dealing with the situation, but in any case most Traffic Patrol specialists with the knowledge to deal with this have been replaced by far cheaper and much more profitable traffic cameras. Also if your working to meet targets it’s far easier to hit the generally law abiding in order to maximise your ticket count rather then end up spending the afternoon getting some old nail removed to a car pound, and waiting in a Police Station Custody area for hours with the driver for a foreign language interpreter and duty solicitor to arrive (you can add Appropriate Adult, Social Worker and Police Docter if they claim to have Mental Health Issues). Its human nature you take the easy route. Someone tell me this is not true, but trust me it is.