The threat of flight restrictions from volcanic ash has been reduced with the introduction of new measures allowing planes to fly when there is more ash in the air.

After weeks of misery for airlines and passengers, the new Time Limited Zone (TLZ) will allow airlines to resume a more normal schedule, because they can now operate in all but the densest ash clouds.

The new rules have effectively doubled the safe operating threshold of ash acceptable by engines, the Civil Aviation Authority said.

To operate in the new zone, airlines need to present them with a safety case that includes the agreement of their aircraft and engine manufacturers.

UK airline Flybe is the first to achieve this and will be able to use the new zone from midday.

Air traffic control company Nats said: "As a result of this change, there are no predicted restrictions on UK airspace in the immediate future."

Ed Anderson, chairman of the Airport Operators Association, said: "The moves by CAA and Flybe represent a step in the right direction, and will be welcomed by passengers and airport operators alike. We look forward to further positive announcements, each of which will go some way to building public confidence in this important industry."

Flybe chief executive Jim French said: "The application of these new rules in the last 48 hours would have reduced our levels of cancellation from 380 flights to 21, or put another way, only 3% of our programme would have been affected.

"This level of cancellation would be more akin to a weather event and therefore much more bearable for customers and the industry."

Transport Secretary Philip Hammond said: "I welcome this move from the CAA to get more people flying. I know they have been working extremely hard, alongside aircraft and engine manufacturers and airlines, since volcanic ash first entered UK airspace last month. The CAA's work with the industry remains ongoing and I hope to see further progress over the coming days."