People around Watford heard “the loudest planes ever” as the RAF simulated an aircraft hostage scenario overhead.

The Royal Air Force and Metropolitan Police took part in a planned training exercise overnight on Friday (November 17) to test a multi-agency response to a potential aircraft hijack.

Heathrow Airport let people know about the likely noise levels before it began via social media and people in Bushey, Watford, and Kings Langley were among those who were shocked by the noise from the jets.

A Watford resident called them "the loudest planes ever" while others added that they were "scared" and "concerned" not knowing what caused the noise.

Exercise Night Star involved RAF Typhoon jets being scrambled from RAF Coningsby, Lincolnshire, to escort a passenger aircraft to Heathrow. Online flight trackers suggest that one of the Typhoons passed over Watford during the night while another passed over both Bushey and Amersham.

Heathrow director of operations Dale Reeson said: “Simulating lifelike scenarios at the airport and running regular resilience training is an essential part of our preparedness planning.

“We worked in close collaboration with the Met Police and RAF as part of last night’s scenario, and the learnings we’ll take from the joint exercise will only help to further strengthen our crisis response capabilities.”

Met Police confirmed that the exercise was not in response to any specific threat or intelligence. Once the plane landed, officers met the aircraft and hostage negotiators as firearms officers boarded the 160-seater plane.

Chief Superintendent Ian Howells said: “All year round, the Met arranges and takes part in exercises to put the specialist training of officers to the test, in a range of different scenarios.

Watford Observer: An RAF Typhoon jet takes off on a another training exercise at Amari Airbase in EstoniaAn RAF Typhoon jet takes off on a another training exercise at Amari Airbase in Estonia (Image: PA)

"Exercises such as this allow us to ensure that, with our partners, we are well-prepared to respond to all types of emergencies - at our airports, or elsewhere in the capital.”

RAF wing commander Wilkinson said: “Exercise Night Star has provided the rare opportunity for a fully joint and multi-agency end to end assurance of the UK’s air defence and counter terrorism response.

“Each participating unit has used the exercise to hone their skills and improve their procedures to continue to ensure aviation safety.”