Boris Johnson has tasked Michael Gove with leading a review into using vaccine passports.
The prime minister has performed a U-turn on the passports, after saying as recently as last week that people would not need one to go to the pub.
Critics have described the idea as discriminatory, but Cabinet Office minister Gove will examine if they can help ease England out of its coronavirus lockdown.
On Tuesday, Johnson said: “This is an area where we’re looking at a novelty for our country, we haven’t had stuff like this before, we’ve never thought in terms of having something that you have to show to go to a pub or a theatre.
“There are deep and complex issues that we need to explore, and ethical issues about what the role is for government in mandating or for people to have such a thing or indeed in banning from people doing such a thing.
“We can’t be discriminatory against people who for whatever reason people can’t have the vaccine, there might be medical reasons why people can’t have a vaccine.”
Johnson said the “proper review into the issue”, led by Gove, will obtain “the best scientific, moral, philosophical, ethical viewpoints on it and will work out a way forward”.
The prime minister announced the review on Monday while outlining his roadmap for England’s exit from lockdown.
He said the government wanted to determine whether offering “COVID status certificates” could help venues to open again.
During a Downing Street briefing, Johnson acknowledged there were ethical issues around vaccine certificates.
He said: “There are clearly some quite complex issues, some ethical issues, issues about discrimination and so on, to what extent can governments either compel or indeed forbid use of such certification.
“There may well be a role for certification but we just need to get it right.”
Watch: Could rapid Covid testing help entertainment venues reopen?
It is hoped the findings of the vaccine passport review will be available before 21 June, the earliest date by which ministers hope all restrictions can be lifted.
If the review signs off on the use of COVID status certificates, it could mean venues or businesses could deny someone access if they cannot provide evidence that they have been vaccinated against or tested negative for coronavirus.
Campaign group Liberty warned that vaccine passports could create a “two-tier society”.
On Tuesday, Dr Zubaida Haque, a member of unofficial Independent Scientific Advisory Group for Emergencies (Sage), said: “Until everyone who can have the vaccine, is vaccinated, vaccine passports will only serve to create division, discrimination and resentment.
“Will businesses, hotels, bars, cinemas be able to turn non-vaccinated people away? Can an employer demand you're vaccinated before working?”
The prime minister announced on Monday that all COVID-19 restrictions on social contact will be lifted on 21 June at the earliest.
In his roadmap for exiting the lockdown, he said families can visit indoors and stay overnight from 17 May at the earliest.
Johnson outlined five key dates for easing restrictions in the months ahead.
The first step of the plan will see all schools in England reopen from 8 March, with wider use of face masks in secondary schools.
Socialising in parks and public spaces with one other person will also be permitted from that date.
Watch: Boris Johnson 'very optimistic' all restrictions will be lifted by 21 June