Boris Johnson’s government will make the use of Covid “passports” mandatory for all nightclubs in England if venues owners do not use certification voluntarily, No 10 has said.

       Thousands of people danced the night away at “Freedom Day” parties starting at midnight after venues were given allowed to open for the first time in almost 18 months.

       Asked about concerns that clubs will help the virus spread, Downing Street said venue owners may still be forced to use certification so clubbers can prove they are fully-vaccinated or have tested negative.

       “We encourage nightclubs to use the Covid pass – many of them having been using it in pilots,” said the prime minister’s official spokesperson on Monday. “We will certainly consider mandation if necessary.”

       The No 10 spokesman added: “We encourage [venues] to use certification. We are reserving the right to mandate certification in certain venues – maybe at a later date if necessary, and we will keep that under review.”

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       Julian Tang, a clinical virologist at the University of Leicester, warned that nightclubs are potent spreading grounds. He said their core customer base, people 18 to 25, is “not fully vaccinated – they’re not masking”.

       He added: “They’re in very close contact, heavily breathing, shouting very loudly to the music, dancing with different people. That’s the perfect mixing vessel for the virus to spread and to even generate new variants.”

       The government wants nightclubs and other venues to check whether customers have been vaccinated or have a negative test result. There is no legal requirement for them to do so, however, and most say they won’t.

       “They should be using the Covid pass which seeks to mitigate that [transmission] risk – it is very much in their interests,” Mr Johnson’s spokesman warned.

       Asked whether clubs could be closed again if the third wave made it necessary, the No 10 spokesman said: “That would be a significant step. Our approach is to work closely with those businesses and encourage them to use that certification.”

       Michael Kill, chief executive of the Night Time Industries Association, said many owners see certification as a huge turn-off for customers – and accused the government of “passing the buck” to businesses.

       “Either mandate it or don’t mandate it,” Mr Kill said, calling for more clarity. “This is putting an inordinate amount of pressure on us.”

       No 10 also confirmed on Monday that the government will not be tweaking the sensitivity of the NHS Covid app – despite concerns the “pingdemic” is causing serious staff shortages.

       Asked if the government had dropped the idea of tweaking the sensitivity of the app, the prime minister’s spokesman said: “That’s correct.”

       He added: “The app is doing what it is designed to do – informing close contacts that they are at risk and advising them [to self-isolate].”