On Monday, 8 December, officers arrested a 24-year-old man in Lambeth on suspicion of robbery and assault at and a 23-year-old woman on suspicion of conspiracy to commit robbery. They both remain in custody.

The arrest follows an investigation into an assault at the multi-storey car park at Heathrow Airport's Terminal 3 on Sunday, 7 December.

Police were called at 8.11am on Sunday following reports of a number of people injured by a noxious substance.

The London Ambulance Service treated 21 people with injuries, including a three-year-old child who was treated at the scene. Five people were taken to hospital.

Their injuries are not believed to be life-changing or life-threatening, and all have now been discharged.

An investigation was launched which has established that, prior to the assault, two women were robbed of their suitcases after getting out of the car park lift.

During the robbery, the men sprayed a substance, believed to be pepper spray in the direction of the women. This substance affected those in the vicinity, causing minor injuries.

On Sunday, officers arrested a 31-year-old man on suspicion of robbery and assault close to the scene.

He has since been released under investigation while enquiries continue.

Commander Peter Stevens said: "Our team have been working at pace today to review CCTV from the area and speak with witnesses at the scene.

"At this stage, it's understood that a woman was robbed of her suitcase by a group of four men, who sprayed a substance believed to be pepper spray in her direction.

"This occurred within a car park lift, with those in the lift and surrounding area affected by the spray.

"Our officers are working to determine the full circumstances around what happened but we do believe this to be an isolated incident with those directly involved known to each other.

"We appreciate that this has been a concerning incident and I commend the actions of the emergency services and members of staff at Heathrow Airport."

Enquiries remain ongoing and anyone with any information is asked to contact the investigation team on 101 quoting CAD 1803 7 DEC or anonymously via Crimestoppers on 0800 555 111.