Timeline of Boris Johnson's battle with coronavirus

British leader Boris Johnson was on Monday back at work in Downing Street, after two weeks' convalescence following hospital treatment for coronavirus which included three days in intensive care.

Here's how the COVID-19 crisis has unfolded for the prime minister:

Johnson has been criticised for initially not taking the coronavirus seriously enough -- on a personal and political level.

As the outbreak began to spread beyond China through February, he spent a week at the government's country estate home, Chevening, reportedly with his partner Carrie Symonds.

By early March, with more than 100,000 cases recorded globally and the World Health Organization (WHO) warning of a potential pandemic, he still appeared to be underestimating the threat.

"I continue to shake hands," Johnson said at a March 3 press conference, after visiting a hospital ward and meeting patients of the COVID-19 illness.

Two days later, Britain's first death from coronavirus was announced.

With the number of confirmed coronavirus cases climbing over 1,000 by mid-March, Johnson was still insisting rigorous hand-washing was the best defence.

He remained unwilling to introduce the kind of lockdowns seen in Italy and elsewhere, and confusion surfaced over strategy.

The government said it was aiming to suppress the number of cases to stagger demand on the state-run National Health Service (NHS).

But its chief scientific adviser also suggested allowing some "herd immunity" to develop in the population was part of the strategy.

On March 20, Johnson's government dramatically escalated its response, ordering all schools, pubs, restaurants, gyms and other social venues to close across the country.

Three days later he addressed the nation on television, telling Britons they should only go outside to buy food, to exercise once a day or go to work if they absolutely cannot work from home.

But he and his ministers continued to conduct some meetings in person, despite reports staff in Downing Street were self-isolating after developing coronavirus symptoms.

On March 27, Johnson revealed he had tested positive for COVID-19 after developing mild symptoms the previous afternoon.

The Conservative leader embarked on seven days of self-isolation, as advised by British health officials, in his flat above his Downing Street office.

But on April 3, he said he would be remaining in isolation at home as he had failed to shake off a high temperature.

After nine days of persistent symptoms, Johnson was admitted to hospital on April 5 as a "precautionary step" for further tests.

Within 24 hours he was moved to an intensive care unit, in case he needed to use a ventilator. Foreign Secretary Dominic Raab stepped up to deputise.

Johnson spent three days in the unit, receiving "oxygen support", but he was not put on a ventilator.

He admitted after discharge on April 12 that his fight with the virus "could have gone either way".

Johnson credited the NHS with saving his life -- "no question".

He has spent the past two weeks recovering at Chequers, the country home of prime ministers, northwest of London.

Last week he held phone calls with US President Donald Trump and Queen Elizabeth II, but officially remained off work.

Johnson returned to Downing Street on Sunday and on Monday was due to chair the government's daily coronavirus meeting.

In his first public appearance in nearly a month, he read a statement outside his office saying Britain was "beginning to turn the tide" in tackling the virus and urged people to maintain the lockdown.