London (CNN) Boris Johnson is back.

The first world leader known to have had coronavirus is now leading his nation's response to it, and in a speech outside 10 Downing Street, the British Prime Minister had a clear message: Don't give up on the lockdown yet.

In his first remarks after returning to work Monday, Johnson acknowledged that the restrictions were hard to bear and risked taking a heavy toll on the economy.

But he warned that the UK was at "the moment of maximum risk" and suggested restrictions would need to remain in place for the time being in to avoid a second peak of infection. The UK's lockdown measures are due to be reviewed again by May 7.

Johnson struck a characteristically upbeat tone in his address, drawing on his own brush with the virus to offer a message of hope to a country which has endured at least 20,000 deaths from the virus and where the government has faced heavy criticism for its early response.

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