MICHAEL HOLDEN and ALISTAIR SMOUT THE United Kingdom has recorded its highest daily death toll since the start of the COVID-19 pandemic as London declared a major incident, warning that its hospitals were at risk of being overwhelmed. With a highly transmissable new variant of the virus surging across Britain, Prime Minister Boris Johnson has shuttered the economy and is rushing out vaccines faster than the country's European neighbours in a bid to stem the pandemic. Britain has the world's fifth-highest official death toll from COVID-19 at nearly 80,000, and the 1,325 deaths reported within 28 days of a positive…