A government-commissioned report in December examined how Covid certificates could be used to decide whether people should be allowed into sports events, pubs and other crowded spaces, months before ministers publicly confirmed the plan.

A document prepared for NHS test and trace and seen by the Guardian shows that the research also looked into whether certificates could be made a condition of entry for family events such as weddings or even small casual gatherings.

The report, dated 17 December, was prepared by staff working for Zühlke Engineering, a Swiss-based consultancy that has worked closely on the UK’s Covid contact-tracing app, and has a number of staff embedded within the test-and-trace team.

It details research into possible public attitudes to a Covid certificate, sometimes called a domestic Covid passport. This would use vaccination status, a recent negative Covid test or proof of coronavirus antibodies to allow people into potentially packed places when the country opens up.

The document includes mock-up pictures of how an app-based Covid certificate might work, using scannable QR codes. One shows this on the main NHS app, with a countdown showing when the pass expires.

Another shows the certificate attached to the NHS test and trace app. This option is seen as unlikely, because the test and trace app is anonymous while the certificate involves personal information.

Covid certificates are enormously controversial. At least 40 Conservative backbenchers are among 70-plus MPs who announced last week that they would oppose them.

There has been considerable speculation about the use of such certificates, but as recently as February the vaccines minister, Nadhim Zahawi, said the government was “not looking at a vaccine passport for our domestic economy”.

Boris Johnson is expected to announce the initial findings of a review into the subject on Monday, but not to say categorically whether or not they will be introduced.

The December document uses focus group research to highlight public attitudes towards the idea. It found that people considered them potentially useful for events such as football matches and even weddings, but not for smaller family gatherings.

Concerns raised included the amount of planning needed, whether test results would arrive on time and worries that people might act more recklessly if they had a certificate.

Civil liberties groups have spoken out against the idea of Covid certificates. Silkie Carlo, the director of Big Brother Watch, said they would be “the first attempt at a segregation policy in Britain for decades”.

She said: “They would exclude and disadvantage the most marginalised people in our country, dividing communities without reducing risks.”