Government sources have suggested an announcement on travel corridors could be made tonight or tomorrow morning, but the industry remains in the dark.

A source at Number 10 reportedly briefed journalists today on the imminent announcement, with travel to countries with corridors in place to resume without quarantine restrictions from July 4.

However, an aviation source said: “Different government departments are briefing different things. The latest [briefing] is that the prime minister could announce something Friday evening and the travel corridors will be to all of Europe.

“But it could just be an announcement to say ‘Air bridges are coming. More detail to follow.’ We’re taking everything with a pinch of salt. The industry has heard nothing from the government.”

The source said: “We’re operating on the basis that [transport secretary] Grant Shapps will set out the detail on Monday in Parliament.

“We expect Mediterranean destinations to be front and centre [of the initial corridors].”

It had been expected the government would announce corridors to about 10 EU countries initially, with expansion to the rest of the EU later in July.

The source noted: “The Schengen Area is opening up from July 1 so it is almost immaterial where [in Europe] the government decides to include.

“It will be difficult to say ‘You’re not allowed to travel to Bulgaria’ when you can travel elsewhere in Europe.”

Shapps told the transport select committee of MPs on Wednesday: “We will say something about air bridges on June 29. The announcement will be made in Parliament first.”

The source noted: “Shapps will face an angry Parliament if this is announced over the weekend. But it would be no skin off Number 10’s nose to throw him to the wolves.”

A second aviation source said: “We’ve not heard anything. It’s appalling. We’re working on a Monday announcement for a July 4 implementation, but we have no confirmation.

“We will be very disappointed if the papers are given a pre-briefing and the industry is not.”

The source added: “We’ll be looking at the number of corridors. Talk of 10 is pretty lame. Will the government provide transparent criteria, because every airline will want to see them?

“If there are only 10 corridors you would have to question the criteria.”

Shapps outlined some of the criteria to the transport select committee this week, telling MPs: “[It depends] not only what the level of disease is, but also what the trajectory is.

“Do they have something similar to our NHS Test and Trace system in place? Do they have the testing capability? Then what are their social distancing rules?”

Another source described the corridors agreements as “a patchwork”, saying: “In some cases, Britain will simply say it will allow in visitors from a country. With others, they have negotiated specific agreements.”

An airlines source said: “The lack of certainty is causing a lot of problems. Working to a date and to some criteria is the absolute priority.

“A lot of airlines have taken a punt and taken decisions anyway. They just could not wait. But it is no way to do things.”

The source noted: “There are places where travel restrictions are probably warranted. But what happens to some long-haul markets? It’s going to be tremendously difficult.”