There has been a lot of confusion surrounding driving requirements for Ukrainians staying beyond 6 months with their car in the UK.
As things stand, if you bring a car into the UK you will have to register and tax your car in the UK after 6 months.
A detailed explanation of driving requirements and licensing is available at the website put together by the London based group Help for Ukrainian Refugees; you can change the language settings to Ukrainian at the top of the page.