A growing number of Conservative MPs are threatening to boycott this year's party conference if they are forced to have vaccine passports as a condition of entry.
Lockdown-sceptic Tories are incensed at suggestions that only people who are double jabbed with a Covid vaccine will be allowed into the gathering in Manchester in October.
The news came as Cabinet ministers said there had been a big increase in over-18s coming forward for jabs after Boris Johnson threatened to make them a condition of entry at nightclubs from September.
That came as Nadhim Zahawi, the vaccines minister, said ministers could "mandate the double vaccination requirement for nightclubs, crowded unstructured indoor settings, large unstructured outdoor settings and, of course, the very large events such as business, music hall, and spectator sports events".
Tories on the party's libertarian wing were spooked by the Mr Johnson's announcement on Monday that he would change the law to require proof of two doses of a Covid vaccine for entry into nightclubs and "other venues where large crowds gather" by the end of September – just before the start of the conference.
The Telegraph disclosed on Thursday that there were fears party chiefs could make proof of a jab a condition of entry at the conference, which runs in Manchester from October 3 to 6.
The report prompted half a dozen Conservative MPs to say they would refuse to attend, including Sir Charles Walker, a former member of the party's board, Mark Jenkinson, Chris Green and Peter Bone.
Mr Bone told the Guido Fawkes website: "I can confirm that I won't be attending the party conference if we have to have a vaccine passport to attend."
Mr Green said: "I would love to go to the party conference because it is in Manchester, down the road from my constituency and a great chance to champion levelling up, but I will not be attending in person or online."
Amanda Milling, the Tory party chairman, confirmed that MPs had been in touch to express concerns about the need for vaccine passports. A party spokesman said: "The party will be following government guidance."
At least 42 Conservative MPs have already signed a petition opposed to Covid certification being used for "general services, businesses or jobs".
If it were put to a vote, a rebellion on that scale could be enough to overturn Mr Johnson's Commons working majority if all other opposition MPs voted against the measures. Labour is also considering voting against.
Cabinet ministers are hoping that vaccine passports might not be necessary because of a spike in young people coming forward to be vaccinated. Internal government figures show that twice as many over-18s came forward after Mr Johnson warned that he may bring in proof of jabs in September.
The hope is that if the proportion of the over-18s with the jab increases from about 60 per cent to 80 per cent, the need for vaccine passports can be avoided. A Cabinet minister said: "If we got to 80 per cent, there is no need to do it. Young people are keen, but you need to get their backside into the queue."
Speaking in the Commons, Mr Zahawi emphasised the need for more young people to get jabbed this summer, saying he wanted to "urge everyone to come forward and get both doses to protect yourself, protect your loved ones, and your community".
He said: "At the end of September, we plan to make full vaccination a condition of entry to those high-risk settings where large crowds gather and interact. By this point, everyone aged 18 and over will have had the chance to be fully vaccinated, and so everyone will have that opportunity to gain the maximum possible protection.
"So, as a condition of entry to these venues, people will need to show that they are fully vaccinated, and proof of a negative test will no longer be sufficient.
"This is not a step that we take lightly. But we will always keep these measures like all our measures under review, with the goal of returning to the freedoms that we love and cherish."