LONDON — The UK transport secretary said on Wednesday that the country's National Health Service (NHS) app will be used as a certificate for international travel, noting that the earliest possible date to "unlock" international travel would be in mid-May.

Under current coronavirus restrictions, it is currently illegal to travel abroad from the UK for holidays.

The existing NHS app is being “re-deployed” to be able to “show you've had a vaccine or you've had testing,” Grant Shapps told UK broadcaster SKY.

The UK government is expected to set out this week which countries people in the UK can travel to this summer.

Shapps said he will set out "towards the beginning of May" which countries fall into the various different categories of a "traffic light" system recently announced by the UK government.

Under the "cautious" plan, countries will be classified as red, amber or green — depending on their pandemic situation.

Countries included in the green list will be ones "where you'll be able to go to without needing to quarantine on your return," Shapps said.

He added that travelers will still need to take a pre-departure COVID-19 test and another one on return.

The earliest possible date to "unlock" international travel is May 17, Shapps said, and that "so far the data does continue to look good from a UK perspective, notwithstanding those concerns about where people might be traveling to and making sure we're protected from the disease being reimported."

The transport secretary added that he is working with "partners across the world to make sure that (the NHS) system can be internationally recognized, as that's the way forward," and that at an upcoming meeting of the G7 secretaries of state for transport, he would be discussing the subject with his counterparts, including transport secretaries from the US and Canada. — CNN