A man has been arrested at Heathrow Airport after a detonation of tear gas caused 20 people to fall ill.

Specialist officers in hazmat suits arrived at the scene following reports that tear gas had been discovered at Terminal 4 on Monday afternoon.

The long-haul terminal was closed for a number of hours as authorities investigated the circumstances surrounding the gas.

On Monday, a source from the Met Police claimed to the BBC that the ordeal was a "mass hysteria event" - however, the force has since denied the report.

The long-haul terminal to be closed for a number of hours as the authorities investigated the circumstances surrounding the incident

A "mass hysteria event" is a type of social phenomenon where a group of people develop similar symptoms, despite the absence of a physical cause.

A spokesman for Scotland Yard confirmed on Tuesday that a 57-year-old had been arrested on suspicion of causing a public nuisance and possession of a firearm.

The terminal was shut down for over three hours, causing delays for thousands of travellers.

The force confirmed that it was not treating the incident as terrorism-related, while the suspect has remained in custody while the ongoing investigation was being carried out.

A spokesman for Scotland Yard confirmed on Tuesday that a 57-year-old had been arrested on suspicion of causing a public nuisance and possession of a firearm

The majority of passengers who displayed symptoms were treated at the scene by emergency services, but the London Ambulance Service said one person was taken to hospital as a precautionary measure.

A spokesman for the Met Police said: “On Monday, September 8 at 4.56pm, police were called to a potential hazardous materials incident at Heathrow Airport Terminal 4.

“Specialist officers attended the scene alongside the London Fire Brigade and London Ambulance Service and conducted a thorough search of the area.

"Following the search, Met officers located a canister of what is believed to be CS spray.

The majority of passengers who displayed negative symptoms were treated at the scene by emergency services

"It is thought that this substance caused a reaction to those within the airport.

“Around 20 people reported to paramedics after the (believed) CS spray caused irritation.

"It has been confirmed that the spray did not cause any life-changing/threatening injuries.

“Following urgent enquiries, a 57-year-old man was arrested on suspicion of possession of a firearm (CS spray) and causing a public nuisance on Tuesday, September 9.

“He remains in police custody. The incident is not being treated as terrorism-related. The investigation remains ongoing.”

A Heathrow Airport spokesman said: "We are very sorry for the disruption caused. The safety and security of our passengers and colleagues is our number one priority."

Exposure to tear gas can cause burning sensations and irritation in the eyes and skin to those who come into contact with it, alongside excessive blurred vision, coughing and chest-tightness.

It is typically used by police units overseas during riots or civil unrest to enforce compliance.