The NHS app may not be ready for use as a vaccine passport when international travel resumes, Downing Street has admitted.

Holidaymakers visiting most popular foreign destinations will be required to show evidence that they have been vaccinated, received a recent negative test or have coronavirus antibodies.

Transport Secretary Grant Shapps has previously said the NHS app – which is currently used to book medical appointments and order repeat prescriptions – will be able to display evidence that someone in England has been vaccinated or tested.

But the Prime Minister’s official spokesman indicated that officials are working on alternative plans for when international travel resumes, which is expected on May 17 for people in England.

“Mr Shapps set out the approach we are looking to take,” the spokesman said.

“Obviously we will be able to confirm ahead of the 17th at the earliest what measures are used for those initial countries that are available for travel, be it the app or another approach.”

The spokesman added: “There are other routes to achieving the same end-goal. We are working on the app at the moment, at pace, to have it ready, and we will be able to confirm ahead of the 17th at the earliest what approaches we will be using.”

Henk van Klaveren, head of public affairs at trade body The Airport Operators Association, said enabling the app to prove a user’s vaccine status “should be a relatively simple technical step” but he is “not as confident” about whether it will integrate test results.

He told the All-Party Parliamentary Group (APPG) on Coronavirus it “has to be the case” that the UK has a “four-nation approach” to the issue.

He said: “From Wales, Northern Ireland and Scotland there is currently no road map on how international travel will restart.

“And similarly, there is no approach at the moment on a four-nation basis for a vaccine passport.”

Premier League executive director Bill Bush told the hearing that “we do support some form of certification for our events”, suggesting that the alternative was restrictions in the form of social distancing and smaller crowds.

He described a form of certification, provided it was voluntary, as “burdensome” but an “acceptable” way to allow fans to attend matches.

Professor Stephen Reicher, from the University of St Andrews and a member of the Sage sub-committee advising on behavioural science, told the APPG that vaccination of white people is “much higher” than black people, and urged the Government to be “very careful not to exacerbate that” in relation to the use of coronavirus passports for domestic use, such as to gain entry to a pub or restaurant.

He said: “If a particular intervention, a particular form of vaccine passport, creates alienation and undermines the level of vaccine take up, then it’s counterproductive, then that limits our ability to make people safe and limits our ability to reopen our society at every level.”

He added: “There’s a real danger that this pandemic will become a pandemic of inequalities, with certain pockets of marginal communities, of deprived communities, in which people are more exposed and in which people are less vaccinated.”

Karren Brady, member of the APPG and vice-chair of West Ham United Football Club, said: “Sadly, serious questions remain over how Covid passports would work and how effective they would be, whether for domestic events or international travel.

“We still don’t know how long immunity from vaccines lasts, whether a streamlined digital system can be introduced in time for this summer and if it will include Covid test results.

“The UK Government should work with the aviation and events industries to provide answers to these practical challenges.”