Boris Johnson has urged people to exercise “extreme caution” when he lifts Covid-19 legal restrictions next Monday, as he shifted responsibility for tackling the rapidly spreading virus to companies and individuals.

The prime minister wants to end “government by diktat” by scrapping most remaining Covid laws but some business leaders fear they are being left in an invidious legal position by ministers, without clear guidance on what to do next.

While companies will be expected to continue imposing anti-Covid measures, Johnson suggested legal restrictions could be reimposed if the public became “demob happy”.

He added: “In order to have an irreversible road map, we also have to have a cautious approach.”

While ministers this month boasted about throwing their face masks in the bin at the earliest opportunity, Johnson struck a more cautious tone amid warnings that daily infection numbers could soon hit 100,000.

People in crowded situations — including public transport and shops — would be expected to wear face coverings, but there would no legal requirement to do so.

Similarly Johnson said proprietors of “nightclubs and other venues with large crowds” would be expected — but not legally obliged — to use the NHS Covid pass to screen customers.

The “work from home” rule will be scrapped on July 19, but Johnson issued a caveat, saying that “we don’t expect that the whole country will return as one to their desks from Monday”.

Claire Walker, co-executive director of the British Chambers of Commerce, said: “Firms have been told to make their own judgments on which Covid-secure measures to keep and which to ditch.

“But they are not public health experts and advice from government is needed. In particular, the government must give clarity on the issue of employment law, health and safety requirements and liability.”

Ministers will publish more guidance to businesses in the coming days.

Matthew Fell, the CBI’s policy director, said the government had to soften self-isolation rules for people who had been in close contact with someone suffering from Covid to avoid disrupting business.

Media talk of “freedom day” on July 19 has been replaced by a realisation in Downing Street that the public, according to opinion polls, would favour a more gradual approach to lifting final restrictions.

Chris Whitty, chief medical officer, said there was “no such thing as an ideal date” for ending legal restrictions, but said that “going slowly” was the most important thing to keep the disease under control.

Whitty has advised Johnson that it is better to move now than to wait until the autumn when NHS hospitals would be under greater pressure. Johnson spoke of the “natural firebreak” of the school holidays.

The key to the decision is the vaccine rollout. Whitty said people with two doses were 90 per cent less likely to go to hospital and 75 per cent less likely to infect someone else.

Pat Cullen, the Royal College of Nursing’s acting chief executive, said when cases were rising across the UK, “we must not lose the benefits of a successful vaccine programme to rash decisions”.

She added: “Public mask-wearing is straightforward and well-established — government will rue the day it sent the wrong signal for political expediency.”

Dr Layla McCay, director of policy at the NHS Confederation, said pressure on health services was already rising. Healthcare leaders compared the levels to those normally seen in January rather than July.

McCay highlighted “a real risk that dropping the restrictions, including to wear masks, especially in healthcare settings, and to socially distance will lead to a significant Covid-19 surge which will place even more strain on a system struggling to cope”.