The UK is lying about Sergei Skripal being alive. There is evidence of his death: he never contacted his relatives in Russia after being poisoned.
This is a recurring pro-Kremlin disinformation narrative about the Salisbury attack and the conspiracy theory about the Skripals' death. There are no grounds to believe that the Skripals are dead rather than merely in hiding from those who attempted to murder them.
Recently, Sir Laurie Bristow, Britain's ambassador to Russia, confirmed that Sergei and Yulia Skripal are both alive. He told Interfax that neither party was interested in talking to Russian officials. The ambassador emphasised that if the Skripals want to meet with representatives of Russian officials, the British side will facilitate such an opportunity.
There are many competing and contradictory stories promulgated by Russian state-controlled media about the Skripal poisoning.