LONDON - No new countries will be added to Britain's green list for international travel when the number of quarantine-free destinations is updated later on Thursday, The Sun reported.

The newspaper, which did not name its sources, also said talks were ongoing to decide whether Portugal, a popular holiday destination for Britons, would remain open for travel.

Airlines and travel companies have been hoping the green list will be expanded, and any failure to add more destinations will be a fresh blow for the tourism industry which had looked to June for a recovery to start.

Britain permitted travel again on May 17 after more than four months of lockdown, but the reopening has to date been very limited, heaping pressure on airlines already weakened by 15 months of lockdowns.

Portugal is currently the only popular European destination where Britons can go without needing to quarantine on their return, providing a lifeline for airlines like easyJet and Ryanair and travel companies like.

If Portugal is removed from the green list, the government will be effectively shutting down international leisure travel once more despite continuing to unlock the domestic economy.

Travel to amber and red countries is not illegal but it is discouraged and many countries on those lists are not open to Britons for holidays, just essential travel or work.

Worries over new more transmissible variants of coronavirus are now threatening the European peak travel summer season, when millions of Britons usually head to southern Europe in July and August.

British Prime Minister Boris Johnson warned the travel industry on Wednesday that protecting the country's vaccine roll-out was his priority.

"I want you to know we will have no hesitation in moving countries from the green list to the amber list to the red list if we have to do so. The priority is to continue the vaccine rollout, to protect the people of this country," he told reporters.

The Sun also said in its report that new countries would be added to the 'red list'.

(Reporting by William James and Sarah Young, Editing by Paul Sandle and Kate Holton) ((william.james@thomsonreuters.com; +44 207 542 3374; Reuters Messaging: william.james.thomsonreuters.com@reuters.net))