World Health Organisation expert Dr David Nabarro says he has “never been more concerned” than he is tonight about the rapidly-worsening coronavirus situation in the UK.The WHO’s Special Envoy on Covid-19 says that even if the Omicron variant of Covid-19 does cause less severe disease than previous variants, the sheer number of cases threatens to overwhelm healthcare systems.He told Sky News that this is an "emergency situation" for the NHS which will get "extremely serious" within the next two weeks – or "perhaps quicker".He added that there was "no way" of knowing how bad the situation will become.He said that he was concerned "not just about the UK, but about the world," adding: "I want to stress the absolute number of people who are.