The British government insisted Sunday that Prime Minister Boris Johnson was "on top of things" as he recovers from the coronavirus facing criticism of his early handling of the crisis.

The Conservative leader spent three days in intensive care after contracting the virus, and has been off work since March 27, but was released from hospital last Sunday after a week-long stay.

Britain's official death toll from the virus now stands at 16,060 after 596 more deaths were reported Sunday, and the country has been under lockdown since March 23, with the government extending it until at least the end of the month.

Education minister Gavin Williamson said on Sunday that "I can't give you a date" as to when schools would reopen.

Recent figures suggest the outbreak in Britain was "starting to plateau", said Jenny Harries, Deputy Chief Medical Officer for England, but warned it was "not fair to say we are past the peak".

Senior minister Michael Gove earlier sought to defend Johnson after the prime minister was accused of being "missing in action" in the early stages of the outbreak.

Johnson "is absolutely on top of things" and issuing instructions, Gove told Sky News. "The prime minister is recovering well, he is in cheerful spirits."

His comments came after a Sunday Times newspaper report said Johnson had missed five of the government's emergency response meetings in January and February.

"None of us expect the impossible, but there are serious questions about why the prime minister skipped Cobra meetings," the opposition Labour Party's shadow health minister Jonathan Ashworth told Sky News. "It suggests early on he was missing in action."

Gove claimed there were inaccuracies in the Sunday Times report, which was based largely on unnamed civil service sources, and that the government would issue a rebuttal.