Britons will find out which countries they will be able to enjoy quarantine-free travel to this summer "in the next couple of weeks" - as the transport secretary confirmed an NHS app will be used as a Covid passport for travel abroad.

Under Prime Minister Boris Johnson's roadmap for lifting lockdown restrictions, international travel without one of the current exemptions - which exclude holidays - will not be allowed any earlier than 17 May.

Ministers have set out plans for a "traffic light" system to be used this summer to categorise different destinations.

And, speaking to Sky News on Wednesday, Transport Secretary Grant Shapps revealed "in the next couple of weeks" he will be able to give details on which countries have made it on to the "green list".

These will be destinations where Britons will be able to travel without having to quarantine on their return, although they will still need to undergo a Covid test before their departure, as well as on their return to the UK.

Mr Shapps also confirmed an NHS app will be used to allow Britons to demonstrate whether they have had a Covid jab, or tested negative for the virus, before travelling abroad.

"It will be the NHS app that is used for people when they book appointments with the NHS and so on, to be able to show you've had a vaccine or that you've had testing," he added.

"I'm working internationally with partners across the world to make sure that system can be internationally recognised."

Government sources clarified the app would not be the NHS Covid app - currently used to "check-in" to venues such as pubs and restaurants for contact-tracing purposes - but would instead be the NHS app used to book general appointments.

Mr Shapps said he was awaiting data from the government's Joint Biosecurity Centre before being able to state which countries would be deemed "green", "amber" or "red" under the traffic light system.

He also warned there was a need to be "very cautious" about allowing Britons to freely travel abroad again.

"Beyond our shores we are seeing the highest levels of coronavirus that we have seen so far in the entire pandemic, right now," he added.

"So we do need to make sure we do this very, very carefully - we don't want to throw away the lockdown, we don't want to throw away our remarkable rollout in this country of the vaccination.

"But, in the next couple of weeks, I'll be able to tell you about which countries will have made it into the traffic light system and that 'green' list in particular are the countries where you'll be able to go to without needing to quarantine on your return.

"You will still need to take a pre-departure test and one test on your return.

"I think people are getting very used to testing now, not least because we provide testing up to twice a week for everyone in the country right now. So I don't think a test itself is a big deal."

Mr Shapps said the government would be monitoring vaccination rates, infection levels, concerns about coronavirus variants, and the accuracy of a country's Covid reporting when deciding how to categorise foreign destinations.

A number of European countries have already said they are hoping to welcome tourists this summer.

Portugal's ambassador to the UK, Manuel Lobo Antunes, told Sky News he was "hopeful" British holidaymakers could be allowed to travel to his country by the middle of May.

Meanwhile, Spain is planning to be ready to welcome back tourists in June.