LONDON -British Prime Minister Boris Johnson will unveil a traffic light system to relaunch international travel on Monday, offering hope for airlines and European holiday resorts struggling in the COVID-19 pandemic.

Johnson has already announced a staggered plan to ease coronavirus restrictions in the months ahead. He now wants to enable international travel to resume without setting back efforts to curb the spread of COVID-19 in Britain.

At a 5 p.m. (1600 GMT) news conference, he will outline a system ranking countries as red, amber or green, based on their levels of infection and vaccination, and on the presence of coronavirus variants.

Noel Josephides, chairman of travel group Sunvil, said the industry ideally needed a month to prepare. He hoped any testing requirements could involve cheaper and rapid tests if customers were going to be persuaded to book.

"The tour operating and travel agency business cannot go through another summer of earning nothing. No one's earned anything for over a year now," he told Reuters.

Britons are among the highest spending tourists in Europe. Josephides said airlines and hotels were waiting to decide whether they would resume operations.

British media suggested countries on the green list, requiring only testing before and after travel, could include Portugal, Malta, Israel, the United Arab Emirates and the United States.

Under the plan, international travel would not resume until May 17 at the earliest. Countries on the amber list would require self-isolation. Those on the red list would require quarantine.

Airlines such as easyJet, Ryanair and British Airways, plus holiday groups such as TUI, hope to avoid a second lost summer but COVID-19 cases have risen in continental Europe.

Johnson is also widely expected to confirm plans to allow all retail, outdoor hospitality and hairdressers to open in England on April 12, with trials of "vaccine passports" taking place to help relaunch mass events.

The government is offering everyone in England two rapid tests a week, to break chains of transmission and spot asymptomatic cases.

"As we continue to make good progress on our vaccine programme and with our roadmap to cautiously easing restrictions underway, regular rapid testing is even more important to make sure those efforts are not wasted," Johnson said in a statement.

Britain has given AstraZeneca and Pfizer shots to more than half the adult population, and the reopening of schools in March has so far caused no spike in cases.

(Editing by Jan Harvey, Emelia Sithole-Matarise and Timothy Heritage) ((kate.holton@thomsonreuters.com; 0044 207 542 8560; Reuters Messaging: kate.holton.thomsonreuters.com@reuters.net))