Conservative MPs have threatened to boycott the Tory party conference if coronavirus vaccine passports are required for entry.
Former minister Steve Baker was among those to say they would not attend the event in October over their outrage that jabs could become mandatory to access crowded venues.
Conservative rebels are planning to ally with Labour to defeat the plan to make full vaccination a requirement of entry for clubs and venues with large crowds from the end of September.
With at least 42 Tory MPs having signalled they would not vote in favour of vaccine passports, the Government faces the real prospect of a Commons defeat.
But regardless of whether they are required by law, the party looks likely to insist they are used at the conference in Manchester in order to set an example.
Workington MP Mark Jenkinson said he was double jabbed and booked for the venue, but added: “I won’t be going to conference if we’re excluding people on the basis of vaccination their status.”
Mr Baker, the deputy chairman of the Covid Recovery Group of lockdown-sceptic Tories, added: “With a heavy heart, and apologies to event organisers, likewise.”
Tory peer Baroness Morrissey said she would join them, and Bolton West MP Chris Green suggested he would too.
A boycott would be an embarrassment for Boris Johnson, who will hope he can get his agenda on track and unify the party after coronavirus forced 2020’s conference online and caused divisions among his ranks.
The Conservatives did not quite confirm that vaccine passports would be used at the conference, but did say: “The party will be following Government guidance.”
Currently, use of the NHS Covid Pass, which can also be used to show negative tests, is not mandatory but is advised “in facilities or events where people are likely to be in close proximity to a large number of people from other households for a sustained period of time”.
Labour said it would not support vaccine passports, criticising the scheme as “costly, open to fraud” and “impractical”, as well as potentially ineffective.
Currently, use of the NHS app to demonstrate whether clubgoers are vaccinated or have had a negative test is voluntary.
No 10 said the Government reserved the “right to mandate” vaccine passports if needed to curb Covid-19 transmission.
Asked whether Boris Johnson was concerned about Tory MPs announcing they would boycott the party conference if attendees were required to prove they had been fully vaccinated, a spokesman for the Prime Minister said: “I would point to what the Prime Minister said specifically about this.
“He said – I think it was on Monday – we reserve right to mandate certification at any point if it is necessary to reduce transmission.
“You’ve heard him and the chief scientific adviser (Sir Patrick Vallance) speak specifically about nightclubs, given the link in terms of the cases we’ve seen in Holland and Israel and other such countries.
“But the Prime Minister also said no one wants to see people being asked to produce papers to visit certain places or take part in activities they enjoy.”