As in the question, car is not mine and I intend to bring it back to EU after a few months when I get myself a new car, is that legal?
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See this other recent question. – Tomas By Jun 12 '19 at 10:14
No. If you become resident in the UK, you must register (and pay tax on) your vehicle within two weeks.
The police are very strict on this as there's a big problem with people registering cars in cheaper countries with less stringent roadworthiness rules, so you're likely to get the car seized if they spot you.
https://www.gov.uk/importing-vehicles-into-the-uk/temporary-imports
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And rest assured this is VERY true, I almost had my car seized but was let off with a warning and I had to go back and show the correct at the police station within 15 days after the warning. – Matt Douhan Dec 16 '19 at 11:10