British Prime Minister Boris Johnson on Monday urged caution as the legal lockdown restrictions come to an end in England on so-called "Freedom Day", even as he remains in self-isolation after coming in contact with UK Health Secretary Sajid Javid who has tested positive for COVID-19.

Johnson warned of the "extreme contagiousness" of the Delta variant of coronavirus, which continues to keep the infection rate in the country at very high levels.

Under Step Four of the government's four-step roadmap to end lockdown, COVID restrictions have now been replaced with guidance emphasizing personal judgment and responsibility on face masks in indoor settings and caution in large gatherings.

"We're doing a big opening up, and that's quite right. If we don't do it now we'll be opening up in the autumn and winter months when the virus has the advantage of the cold weather. We'll lose the precious firebreak we get with the school holidays," said Johnson in a video posted on Twitter.

"If we don't do it now we've got to ask ourselves, when will we ever do it? This is the right moment. But we've got to do it cautiously. We've got to remember that this virus is sadly still out there. Cases are rising, we can see the extreme contagiousness of the Delta variant," he said.

The first lockdown was announced in the UK on March 23 last year. There was some easing in restrictions for the summer months last year before another full lockdown was imposed in January 2021. Since then, there has been a 4-step roadmap to come out of it. Different parts of the UK have followed different norms of easing restrictions.

He reiterated the message for everyone to come forward for their first or second doses, as the "massive" National Health Service (NHS) vaccination program has very "severely weakened the link" between infection, hospitalization, and death.

"So please, please, please be cautious. Go forward into the next step with all the right prudence and respect for other people and the risks that the disease continues to present," he added.

He also used his video to clarify Sunday's U-turn by him and UK Chancellor Rishi Sunak, who first announced they would be taking part in a pilot scheme to be able to continue working from Downing Street despite being contacted by NHS Test and Trace system to self-isolate following Javid's positive COVID-19 test.

''I've been asked to self-isolate by the Test, Trace and Isolate system after I've been in contact with somebody who has COVID, in this case, of course, the Health Secretary Sajid Javid,'' Johnson said.

"We did look briefly at the idea of us taking part in the pilot scheme, which allows people to test daily, but I think it's far more important that everybody sticks to the same rules and that's why I'm going to be self-isolating until Monday 26th July," he said.

Other Cabinet ministers and officials who have also been contacted by the NHS system since Javid's own self-isolation with mild symptoms of COVID-19 are also said to be in quarantine now.

It has led to businesses voicing concerns over what is being branded a "pandemic", where vaccinated people are forced to self-isolate for 10 days after coming in contact with someone who later tests positive for COVID-19.

Ministers are being urged to bring forward the August 16 timeline for such cases to be able to get back to work following a negative COVID-19 test.

The government has already made an exemption for double vaccinated frontline medical staff and care workers to be able to get back to work following a negative test if they are contacted by NHS Test and Trace.

''The government has backed healthcare services at every turn through this global pandemic and these new rules will fortify our collective defenses against this awful virus, by allowing fully vaccinated frontline NHS and social care staff to continue to work when needed," said Javid.

The Opposition Labour Party has raised concerns over the removal of legal mask requirements and the recommendation to work from home where possible as ''reckless'' and warned of a ''day of chaos'' on the transport network as people returned to offices after months away.

''We're doing the right thing to get as close to normal as possible, as quickly as possible,'' said UK Vaccines Minister Nadhim Zahawi.

Other parts of the United Kingdom have varying degrees of lockdown easing rules, with Scotland, Wales, and Northern Ireland all still following mandatory face masks and limited household mixing rules. Meanwhile, in England, there were long queues outside nightclubs as they opened at midnight taking advantage of the new rules.

On Sunday, the UK recorded a further 48,161 coronavirus cases and 25 deaths. This followed an excess of 50,000 cases recorded daily on both Friday and Saturday, the highest since mid-January.

Almost 88 percent of adults in the UK have had the first dose of a COVID vaccine, and 68.3 percent have had both, raising hopes that the infections will not lead to a rapid rise in hospitalizations and death.