Contrary to the absolute nonsense you might read on Social Media and in certain UK shitrags masquerading as newspapers, Putin is not insane, not crazy, not stupid, not "unpredictable", and not a lunatic.
The world has had nuclear weapons for 80 years, through dozens of leaders who had the option to deploy them. None of them have bar Truman, and he certainly wasn't insane or unpredictable.
Putin knows as well as anyone that an indiscriminate nuclear attack on a NATO member would lead to the total destruction of Russia, everything Putin cares about, his legacy, and the future of Russia and the ethnic Russian people, so no, he's not about to go firing nukes at the UK, so you really need to stop fretting about that and get some more help for your anxiety.
Putin could have by now deployed tactical nuclear weapons in Ukraine, because it would certainly expedite the end of that conflict, yet so far there is no sign whatsoever of any intent to do so because even that would provoke international outrage and condemnation, and likely poison already fractious relations with the likes of China, who Russia is going to be increasingly dependant upon given their struggling economy and growing international isolation.