Nightclub customers will need to be fully vaccinated to get gain entry to venues by the end of September, the government has announced.

The prime minister said Covid passports with details of two jabs would become mandatory for people entering clubs, events and “other venues where large crowds gather”.

There will be no option of showing a negative test.

Described as a “hammer blow” to the late-night sector, the measure was announced just hours after the start of so-called freedom day, when the sub-sector was allowed to reopen for the first time in 16 months.

The measure appears to be intended to encourage greater numbers of young people to take up the vaccine.

But there was a furious backlash over the idea of effectively forcing this demographic – who are least affected by the virus physically, but have been among the worst disrupted in their social lives, educations and careers – to take a vaccine in order to resume every day life.

“Nightclubs need to do the socially responsible thing and make use of the NHS Covid Pass as a means of entry,” Boris Johnson said.

The government will make “full vaccination the condition of entry to nightclubs and other venues where large crowds gather” by the end of September, he said.

Michael Kill, CEO of the Night Time Industries Association (NTIA), called the PM’s announcement “another chaotic U-turn”.

“Eighty percent 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.”

In his speech, Johnson said 35% of 18-30-year-olds remain unvaccinated.

He warned of the “continuing risk posed by nightclubs”, despite lifting legal restrictions which allowed nightclubs to reopen.

Chief Medical Officer Patrick Vallance said venues such as nightclubs “are a focus for potential superspreading events” and that has been the case in the Netherlands and Israel, where nightclubs reopened.

He said he expects there will be an increase in cases and outbreaks related to specific nightclubs and urges people to get vaccinated.

However there was ambiguity over the PM’s language, with some comments interpreted as being less stringent than the initial announcement.

Boris Johnson told the press conference: “I don’t particularly want to single out any sector or business, but there is evidence from other countries that they’ve had a particular problem with the opening of nightclubs.

“So what we’re repeating today is we want nightclubs to behave responsibly, use the NHS app.

“We reserve the right to go to mandating for that if we have to. And we may well want to change to a certification regime for that sort of setting… once everybody over 18 has had the opportunity to have two jabs which will be by the end of September.”

Vaccines Minister Nadhim Zahawi first revealed the news of autumn nightclub measures in the Commons earlier yesterday.

Ahead of 10 Downing St press conference, he said everyone 18 and over would have had the chance to be double jabbed by October.

He told the Commons: “We are supporting the safe reopening of large crowded settings such as nightclubs, as we saw last night, and music venues with the use of the NHS Covid pass as a condition of entry to reduce the risks of transmission.

“I encourage businesses to draw on this support and use the NHS Covid pass in the weeks ahead.

“We will be keeping a close watch on how it is used by venues and we reserve the right to mandate if necessary.”

Zahawi added: “Proof of a negative test will no longer be sufficient. Any decisions will of course be subject to parliamentary scrutiny and we will ensure appropriate exemptions for those who have genuine medical reasons of why they can’t get vaccinated.”

Responding to the news, UKHospitality chief executive Kate Nicholls said: “This announcement comes as a hammer blow on a day when nightclubs, a sector that has been closed by the government for 16 months, were finally given hope that they could start to trade viably and make progress toward rebuilding and paying off accrued debts.

“Covid passports will be a costly burden that run the risk of creating flashpoints between staff and customers, as well as raising potential issues with equalities legislation and the handling of customer data. As recently as last week the government asked us to work with them on a voluntary scheme, so this new policy is devastating and risks hitting these fragile businesses and derailing their recovery and costing thousands of jobs.”

Sacha Lord, night time economy adviser for Greater Manchester, said the whole industry had been taken by surprise by the measure.

“I am not a scientist or a doctor, but I am deeply concerned by the discriminatory nature for those who either can’t have the vaccine for medical reasons or age, or who do not want to,” he said. “Surely these answers should have been given at the same time as this announcement.

“Where does this leave festivals or live music events catering specifically for teenagers or children who aren’t being vaccinated? Does this now mean young people, who have already suffered hugely during this pandemic, now won’t be able to experience the thrill of seeing their favourite artist on stage? With this one move, the Government appears to have wiped out live gigs for a whole generation.

“Lastly, there are obvious questions over how these checks will be enforced, and regarding the financial impact on the sectors. How will nightclubs now compete against pubs and bars down the road where these restrictions aren’t needed, or attract punters who can just as easily have a house party without these enforcements in place.

“I have been in the nightlife and events industry for over 25 years, but I cannot see any reason why anyone would now want to enter this sector with such financially damaging restrictions in place.”