[quote=your link]Temporary Imports
It is possible to import your vehicle temporarily and drive with your home registration plate. This is more applicable to expats from the European Union who are living in the UK for under six months. This can be for a single visit or for periods of up to six months in length. The vehicle still has to be registered and taxed in its original country. If an expat becomes a UK resident then the vehicle must be registered and taxed in the United Kingdom immediately
The DVLA link doesn't mention transit plates, but it does mention this:
You can be prosecuted if you use your vehicle on a public road before you complete these steps, unless you’re driving it to a pre-booked MOT or vehicle approval test.
The transit plates don't apply in the UK, and he's not temporarily importing it. If you get a car imported from Europe, and you're a UK resident, you're not allowed to drive it on the foreign plates, legally speaking. Whether you'd get caught or not and whether you'd chance it is neither here nor there. I know this, because I've just imported a car from Europe!
If I was a Frenchman, living in the UK for 4 months for work or something, and brought my car over with me, I would use the transit plates. If I'm here more than six, I can't do it on a temporary basis. If I move to the UK permanently, then I'd have to register the car in the UK straight away.
If you're a UK citizen, and you drive a car in the UK that is registered overseas and with foreign plates etc, then you're breaking the law. That's all there is to it, whether you do it for a year, or whether you're driving back from Dover on the day you collected it. The only mitigating circumstance would be if you insured it on the VIN and booked it in for an MoT. That being the case, you could drive it to the test on the foreign plates.