Prime minister Boris Johnson said he was not ruling out legal restrictions to prevent people flouting health advice to stay at home and keep away from public gatherings.
Measures including the closure of most shops and forcing all but essential workers to remain at home are on the table – after an alarming rise in cases in the capital.
Asked if there could be a shift towards a compulsory lockdown in the worst areas within the coming days, Mr Johnson said he was “a believer in freedom” and thought people should take their own decisions.
But he told a Downing Street press conference: “The more closely and the more strictly, more ruthlessly, we can enforce upon ourselves and our families the advice that we’re getting about avoiding unnecessary gatherings, about staying at home when we have symptoms – all that advice, which is good advice – then the better we will be able to protect our NHS, the fewer deaths we will have and the less suffering there will be in the UK population and the faster we will get through this and the better we will bounce back eventually.
“So it is a very, very clear choice for people this is strong, strong advice. We do not rule out, because it would be quite wrong to do so, taking further and faster measures in due course.”
Mr Johnson’s official spokesman said that current measures – merely advising the public to avoid pubs, restaurants, public transport and “unnecessary” social contact – were only what was considered “necessary at this point in time” and that the government was ready to “do whatever is required to keep the public safe based on scientific and medical advice”.
London is expected to suffer one quarter of the eventual total number of fatalities.
The government is confident it has “masses of powers” to enforce something akin to mass quarantine, even without the emergency legislation about to be passed.
The 1984 Public Health (Control of Disease) Act – strengthened when the crisis broke out – allows for “individuals to be kept in isolation for their own safety”.
The prime minister himself referred, earlier this week, to even having the power to prevent people shaking hands, in extreme circumstances.
Although the UK switched tack to urge the people to accept dramatic restrictions on normal life, it remains way behind most of the western world.
Edouard Philippe, the French prime minister, accused the UK of not playing its part in the “war” on the virus, stating: “Everyone within the European Union must adopt coherent methods and processes to fight the epidemic, as in Italy, France and Spain.”
The UK was taking “too long continuing to avoid these containment measures”, he said – warning they could be repercussions for British visitors to France.
Mr Johnson’s chief scientific adviser Sir Patrick Vallance said that anyone failing to observe advice to avoid unnecessary contacts was “putting lots of people at risk”.
“The modelling does take into account that not everyone’s going to follow it,” Sir Patrick told the No 10 press conference. “But a very high proportion need to.
“We all need to really focus on this, because the moment we say ‘Well, it’s not for me, it’s for somebody else’ and compliance for this goes down, the less effective it’s going to be.
“And the reason this is important - I can’t stress this enough – is to make sure that the NHS ICU (intensive care unit) capacity is kept in a way that we don’t breach it, and the ventilators are available to do this. So when we don’t adhere to this, we’re actually putting lots of people at risk, we’re putting those sickest patients at risk.
“It’s crucial that this isn’t taken as soft advice, but is taken as a really clear instruction to do this, if we’re going to make sure that we protect the lives of others.”
Sadiq Khan, London’s mayor, has protested at not being kept fully informed about the government’s plans, being unaware of whether the lockdown would take place, or what form it might take.
A decision will be based on the latest advice presented to the Cobra emergency committee, but it will not be imposed before Friday at the earliest.
It comes as schools across the UK shut down by the weekend, another measure No 10 has sought to avoid.
The prime minister’s spokesman added: “London seems to be moving ahead of other parts of the UK and he [Boris Johnson] advised people in London to pay particular attention to the measures we have been putting in place.”
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