The use of so-called vaccine passports to decide whether people can enter pubs would go against the “British instinct”, Sir Keir Starmer has said.
The Labour leader told the Daily Telegraph it would be “wrong in principle” to ask landlords to check customers’ Covid jab certificates.
A government review is looking at whether this system could help to reopen the economy in England.
Discussions have been taking place across the devolved nations.
Under the government’s four-step plan to ease England’s lockdown, legal limits on social contact could be lifted by 21 June, if strict conditions are met.
But the prime minister has suggested pub-goers could be asked to provide a vaccine certificate, after all adults have been offered a jab by the end of July.
Currently, anyone who gets an injection receives a vaccination card and the details go on to their medical records.
The “passport” could mean the information being added to the NHS app, allowing mobile phone users to prove to publicans that they have received their injections.
But Sir Keir said: “My instinct is that… [if] we get the virus properly under control, the death rates are near zero, hospital admissions very, very low, that the British instinct in those circumstances will be against vaccine passports.
“I think that this idea that we sort of outsource this to individual landlords is just wrong in principle.”
He added that “this is really difficult and I’m not going to pretend there’s a clear black and white, yes-no easy answer on this”.
But Labour would look at any government proposals before deciding whether to oppose them, he said.
Liberal Democrat leader Sir Ed Davey said the government seemed “utterly incapable of making its mind up on Covid certificates”, adding: “This latest wheeze is the worst of all worlds.”
“As well as burdening struggling pubs with extra cost, the idea that businesses can voluntarily bar certain customers, who may not even have been offered a vaccine, is deeply illiberal,” he said.
Pub industry representatives accused the government of “backsliding” over plans to allow venues to reopen.
In a joint statement, UK Hospitality, the British Beer and Pub Association and the British Institute of Innkeeping warned that vaccine passports could prevent “millions” of young people who have not received their jabs visiting the pub “for months”.
Downing Street said an ongoing review was looking at how testing or vaccination could be used to play a role in opening the economy, and would consider the ethical, privacy, legal and operational aspects.
The prime minister will give an update on the Covid situation on Monday.