Has the UK decided to block or add protectionist regulations to Chinese EV imports?

No. Jaecoo (Chinese but not really an EV company) is the third best selling car at the moment. You see a tonnes of BYDs about. We also have Geely and Leapmotor

many other too, including:

MG is a British car badge, now owned by SAIC China

Volvo and Polestar are owned by Geely

LEVC makes the new EV London black cabs, is also owned by Geely

XPeng and Omoda are present too.

No, at least not yet. It was one of the issues when discussing with EU, as they were worried those EV will get routed through UK to EU without tariff.