United Kingdom nightclubs and venues hosting large gatherings are going to be required to force patrons to be fully vaccinated, Prime Minister Boris Johnson announced in a news conference Monday.

"I should serve notice now that by the end of September, when all over 18s have had their chance to be double jabbed, we're planning to make full vaccination the condition of entry to nightclubs and other venues where large crowds gather," Johnson told reporters in a video posted on Twitter by BBC News.

"Proof of a negative test will no longer be enough."

Johnson himself was speaking from his home during quarantine after being in contact with the British health minister, who tested positive for COVID-19, The Hill reported.

Johnson noted 35% of Britons 18-30 are still not fully vaccinated, which amounts to about three million people who will be impacted by Johnson's mandate, according to BBC News.

"I don't want to have to close nightclubs again as they have elsewhere," Johnson said. "But it does mean nightclubs need to do the socially responsible thing."

Johnson had lifted many of the COVID-19 restrictions despite a rise in cases of late, defending having done so by saying "If not now, when?"

Still, he believes the experimental vaccine is vital to public safety in large gatherings.

Critics of the vaccination mandate, including U.K. Hospitality chief Kate Nicholls, consider it "a hammer blow" to the struggling industries only now trying to get back in business.

"COVID passports will be a costly burden that runs the risk of creating flashpoints between staff and customers, as well as raising potential issues with equalities legislation and the handling of customer data," Nicholls told BBC News.

The U.K. government is "effectively moving to compulsory vaccination," according to conservative Member of Parliament Mark Harper to BBC.

"So, 'freedom day' for nightclubs lasted around 17 hours then," Night Time Industries Association chief Michael Kill told BBC News.

"Leaving aside the fact that this is yet another chaotic U-turn that will leave nightclubs who have been planning for reopening for months having to make more changes to the way they operate – this is still a bad idea.

"80% of nightclubs have said they do not want to implement COVID passports, worrying about difficulties with enforcing the system and a reduction in spontaneous consumers, as well as being put at a competitive disadvantage with pubs and bars that aren't subject to the same restrictions and yet provide similar environments."

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