British and European holidaymakers should be able to visit EU countries this summer but may have to deal with multiple, potentially unconnected health certificates unless the bloc can agree on cost, privacy and technical aspects of a common pass.

Talks on the mechanics of reopening travel routes between the UK and EU countries over the summer holidays are due to open within days, with officials in Whitehall working on a Covid travel pass using the UK’s NHS app.

Under heavy pressure from tourism-reliant countries such as Greece, Spain and Portugal, 20 EU member states plan to start testing a common EU “digital green certificate” next month, with a view to making it live by mid-June.

The scheme should avoid the quarantine and testing requirements currently in force by allowing travellers to store on their phones evidence that they have been vaccinated, recently tested negative, or acquired antibodies after recovering from Covid-19.

However, there are fears national systems may be incompatible, with several countries already developing and trialling their own schemes – including for holidaymakers from the UK.

“If we can deliver politically, the technical solution will be ready in time. If we don’t, we risk fragmentation across Europe, with possibly incompatible national solutions,” the EU’s justice commissioner, Didier Reynders, warned on Wednesday.

“We would risk having a variety of documents that cannot be read and verified in other member states. And we risk the spread of forged documents, and with that, the spread of both the virus and the mistrust of citizens,” Reijnders said.

Spain said on Tuesday it aimed to reopen to foreign tourists, including from the UK, in June, using its own Covid digital health certificate scheme.

The tourism minister, Fernando Valdés, has said his country would be ready for mass tourism this summer, and the certificate would be “fundamental to offering travellers certainty”. Valdés last week said Spain was “desperate to welcome” British visitors.

Portugal has said UK holidaymakers could be allowed back into the country next month. Manuel Lobo Antunes, Portugal’s ambassador to the UK, told Sky News he was hopeful that “from the middle of May, regular mobility between the UK and Portugal and vice versa can be established”.

Greece and Cyprus are both eagerly awaiting British tourists. After championing the idea of “vaccine passports”, Athens has moved aggressively, announcing it will be dropping quarantine requirements and reopening to tourism on 14 May.

From that date, anyone with a negative test or certificate showing they are fully vaccinated will be allowed into Greece without having to self-isolate. Last week, quarantine restrictions were removed for citizens from the EU and five other countries, including the UK.

Anglo-Greek teams have been discussing vaccine certificates for months, with agreement on a digital certificate expected by the summer. Haris Theoharis, the Greek tourism minister, said this week NHS vaccination cards would be accepted in the meantime, but a ministry spokesman told Sky News this was not the case and an “official UK health certificate” would be required.

Cyprus will welcome fully vaccinated travellers from 65 countries including Britain from 10 May after going back into lockdown on Monday following a surge in infections. The deputy tourism minister, Savvas Perdios, told Reuters the island expected clarity on documentation from the UK, its main market, next month.

Italy is expected to announce its rule for foreign holidaymakers in May, but Britons are already booking holiday lets for this summer. “The economic impact of massive vaccination campaigns is very concrete,” Stefano Bettanin, the president of Property Managers Italia, told Corriere della Sera on Monday.

“We’re taking many bookings from Britain and the USA, and it is no coincidence that these are countries where the most vaccine doses have been administered,” Bettanin said. The most popular destinations were Sicily and Puglia, he added.

A tourism ministry spokesperson said that under regulations expected to soon be approved by the health ministry, Italy would open to visitors vaccinated with a vaccine that has been approved by the EU regulator.

France has begun trialling a digital travel certificate for its own tourists on flights to and from Corsica and the French overseas tourists, with the president, Emmanuel Macron, telling US television last week the country aims to welcome tourists from outside the EU this summer. No firm announcements have yet been made.