LONDON (Reuters) - The United Kingdom’s chief medical officers said on Monday there was “a material risk” of the health system in several areas of the country being overwhelmed by COVID-19 over the next 21 days without new measures. The chief medical officers of England, Scotland, Wales and Northern Ireland said in a joint statement that they recommended the UK’s COVID-19 alert level should move from level 4 to level 5. British Prime Minister Boris Johnson was set to announce tougher coronavirus restrictions for England later on Monday.