Noisy Airbus A321s, the preferred aircraft of many budget carriers, have been flying as low as 4,000ft above people’s gardens in Hertfordshire, campaigners say.

It has turned the flightpath into a “motorway in the sky”.

It comes as the airport’s owner is trying to increase capacity from 18 to 36 million passengers a year from 2020, despite planning permission for 18 million passengers not due to expire until 2028.

Andrew Lambourne, of Ladacan, which campaigns for noise control at Luton, said residents should be compensated for the blight caused by the now-proposed 240,000 flights a year.

He said: “People on the ground have been hit by a treble whammy.

“Firstly, a 70 per cent increase in flights on the busiest westerly departure route heading towards eastern Europe, meaning shorter intervals between noise events and more hours in the day affected by flights.

“Secondly, aircraft have steadily got heavier and noisier as airlines have sought to pack in more passengers: A320s and A321s are replacing the smaller and quieter A319s.

“Thirdly, the introduction of RNAV GPS-based navigation, required by a Europe-wide agreement, but portrayed to the local community as being an attempt to reduce over-flights, has resulted in the tracks and the noise becoming more concentrated."

“But residents find that because aircraft noise radiates sideways, the planes are still noisy even if they are no longer directly overhead.”

He added: “The law currently prevents legal redress for aviation noise. That a ‘motorway in the sky’ should be treated similarly in noise and compensation terms to a motorway on the ground seems self-evident.”

Mike Penning, Tory MP for Hemel Hempstead, said planes had been flying so low over his constituency that residents could “read the numbers” on the fuselage.

Complaints from residents living in St Albans, Harpenden and Sandridge have soared in recent months.