LONDON (Reuters) - Prime Minister Boris Johnson ordered England back into a national lockdown after the United Kingdom passed the milestone of one million COVID-19 cases and a second wave of infections threatened to overwhelm the health service.The United Kingdom, which has the biggest official death toll in Europe from COVID-19, is grappling with more than 20,000 new coronavirus cases a day and scientists have warned the “worst case” scenario of 80,000 dead could be exceeded. Johnson, at a hastily convened news conference in Downing Street after news of a lockdown leaked to local media, said that the one-month lockdown across England would kick in after midnight on Thursday morning and last until Dec. 2. In some of the most onerous restrictions in Britain’s peacetime history, people will only be allowed to leave home for specific reasons such as education, work, exercise, shopping for essentials and medicines or caring for the vulnerable. “We must act now,” Johnson said, flanked by his chief medical officer, Chris Whitty, and his chief scientific adviser, Patrick Vallance. “Unless we act, we could see deaths in this country running at several thousand a day.”