Industry leaders anticipate a limited restart to international travel but hope for a wider and less restricted opening by the summer.

Aviation chiefs welcomed government confirmation on Monday of a traffic light system for categorising countries green, amber or red, despite frustration at the lack of detail.

British Airways chief executive Sean Doyle said: “We’re optimistic travel can resume on May 17. [But] we have to look beyond.

“I expect the green list to become quite expansive by the summer. All the indicators are we’ll be in a much better place. We’re confident the situation will improve significantly.”

Doyle insisted: “The PM wants to open up travel. A number of European markets will be open. People can book with confidence.

“The important thing is a detailed framework that we can plan against. The key is the criteria for countries being green or amber.”

Heathrow chief executive John Holland-Kaye agreed: “By the time we get to July, we’ll start to see a lot more countries added to the [green] list and some relaxation of restrictions.”

The system was confirmed in a Global Travel Taskforce update on Monday as Boris Johnson insisted: “I do want to see international travel start up again. We can’t do it immediately, but that doesn’t mean we’ve given up on May 17.”

Countries will be classified according to vaccination rates, infection rates, prevalence of ‘variants of concern’ and the tracking of variants.

Travel will be permitted to ‘green’ destinations without quarantine but with pre-departure Covid tests required before returning to the UK and after arrival. Hotel quarantine will be retained for ‘red’ countries. The ‘amber’ category will mean 10 days’ self-isolation on return and three tests – one pre-departure and two on arrival after two and eight days.

All the requirements will be in addition to testing and quarantine restrictions in destinations.

The government noted: “Countries will move between red, amber and green depending on the data.”

An aviation source suggested: “They’ll announce the green list quite late, maybe a week before [the restart]. That will be unhelpful but makes sense given how bad things are in Europe. We think the list will be small. Everything hinges on what testing regime they put in place.”

One leading industry source argued: “The government plan is coming together. We’d hoped for fewer restrictions, but it was always the case they’d be cautious at the point of reopening. It can be reviewed and we could see a more relaxed regime when the data allows.

“The point of a roadmap is to know what comes next. There needs to be a tiered progression through the system. We want to see what comes after the cautious opening.”

A second source said: “There is concern about the timetable, but why would you put everything at risk to open up quickly when most of the rest of the world is not in such a good place?”

The taskforce report was expected this week. Separately, the government announced the extension of red-list restrictions to Kenya, the Philippines, Pakistan and Bangladesh from April 9.