Millions of people in England could be provided with so-called Covid passports by 17 May to let them take holidays abroad this summer and potentially avoid quarantine when they reach their destination, the Guardian has learned.

The documents – likely to be different from domestic Covid certificates, which the government is working on separately – are still under development but should be made available before restrictions on international travel lift next month, sources said.

With many hoping for a summer getaway, or to see family and friends in other countries whom they have been unable to visit since the pandemic began, pressure is rising on ministers to help ensure that those who have had coronavirus vaccines can prove their immunity to avoid other countries’ entry requirements on isolation and testing.

The transport secretary, Grant Shapps, has said the passports “will of course be a part of international travel” and voiced hopes they would not be viewed as “controversial” – but stressed the need for a cautious reopening given the threat of virus variants.

It came as Public Health England announced 55 more cases had been reported of the variant first found in India, which is due to be added to the UK’s “red list” of countries, with strict curbs on arrivals and a requirement to quarantine in a hotel, from 4am on Friday. There were a further 70 cases of the variant first discovered in South Africa, which is believed to be more transmissible.

A Department for Transport insider said the aim was to roll out a paper or digital document for countries requiring proof of vaccination. Another cautioned it might only be a physical certificate rather than an “all-singing, all-dancing electronic one”, given the time constraints. A third Whitehall source said the Foreign Office was quietly consulting other countries to see whether they would accept certification shown through a repurposed NHS app that is taking longer to develop.

Vaccine passports are not expected to affect the traffic light system planned by the UK government that will grade foreign destinations as green, amber or red for travellers from England – though different rules may apply across the four nations of the UK.

The DfT could announce the lists on 10 May so the data about each country’s Covid case and vaccination rate is as fresh and robust as possible, while giving aviation and tourism businesses some notice to start planning, if the official commencement of international travel is confirmed for 17 May. The criteria for how each country’s colour will be assigned has not yet been confirmed, but countries such as Israel and some Caribbean nations with high vaccination rates are likely to be on the green list.

Following the move last summer to treat countries’ mainlands and islands differently when air corridors were in operation, it is likely the government will pursue a similar approach – meaning that, in theory, Spain could be on one colour list while its Balearic islands could be on another.

To help bring down the cost of PCR tests, which one government figure described as “exorbitant” when multiplied for families travelling abroad, ministers are also considering offering people tests that would be given to them in the UK to take abroad.

A Department for Transport spokesperson said: “We are working on a solution to enable residents to prove their Covid-19 status, including vaccination status, to other countries on the outbound leg. We are working on this as a priority and intend to have the solution ready as soon as possible.”

All foreign travel is currently banned except for a handful of reasons. The bulk of people who come into the UK need to quarantine at a home or other single destination for 10 days. They can be released early if they test negative for Covid on day five.

Spain’s tourism minister, Fernando Valdés, has said the country is “desperate to welcome” UK visitors this summer, and that he wants tourists to “restart holidays” within six weeks.

“I think we will be ready here in Spain,” he said. “We also think that the vaccination scheme in the UK is going pretty well, so hopefully we’ll be seeing this summer the restart of holidays.”

Valdés said Spain was “pushing hard” to persuade the European commission to reach agreements to reopen travel between “third parties such as the UK” as well as EU member states. “If we reach these kind of agreements from the month of June, we will be able to have a summer,” he said.

Saga Holidays, which specialises in holidays for the over-50s, said this week holiday booking enquiries had more than doubled since early April, when the government outlined its plan to restart international travel. The company reported a 127% increase compared with the same period two weeks before.

In December, Cyprus became one of the first countries to say it would waive Covid testing requirements for visitors who have been vaccinated. Seychelles, too, has announced that vaccinated tourists – as long as they have received the complete dose and have certification to prove it – are welcome. Greece has scrapped quarantine rules for UK travellers who have been vaccinated against Covid-19, or those who can show proof of a negative PCR test.

The International Air Transport Association (Iata), which represents the airline industry, has produced a Travel Pass app which would allow passengers to show their vaccine status around the world. It has already been trialled by more than 20 airlines, including British Airways and Etihad, but is likely only to cover air travel rather than cross-border rail or ferry trips.

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