Investigation launched after police force hood over man's head at London Bridge station YouTube/Ayda

A investigation has been launched into British Transport Police officers who tackled a man to the ground and forced a hood over his head during an arrest at London Bridge station. IK Aihie, 20, was detained at the train station on 21 July at 11.30pm after arguing with his girlfriend Jessica McConkey and becoming aggressive toward officers.

While being held, Aihie made a threat that he would spit at officers who then placed a spit guard on him.

Shocked onlookers used mobile phones to film the incident including the moment the guard is placed over Aihie's head.

A clearly distressed McConkey encouraged witnesses to film the arrest and can be heard saying in one clip: "If you have a f****** argument with your girlfriend is that what happens?" More than 500,000 people have since viewed the footage.

She later told the Guardian: "Both IK and I are law-abiding citizens and have the utmost respect for the police force and the work they do. However, in this instance we were treated unfairly and the use of force during IK's arrest was excessive and unwarranted and I have made a complaint to the British Transport Police."

Aihie said it was a "completely terrifying" experience. He has since accepted a caution for an offence under Section 5 of the Public Order Act.

The Independent Police Complaints Commission is investigating whether the BTP officers' action were proportionate. "Following the incident, BTP received a complaint about the conduct of its officers during the arrest and made a voluntary referral to the IPCC," a statement said.

"The IPCC investigation will consider whether the police use of force, the arrest and the method of restraint, including the use of a spit guard, were proportionate, necessary and in line with BTP policies."

IPCC Commissioner Cindy Butts said the incident generated a "great deal of concern and debate"a mong the public and that is was important to investigate.

"This will include considering whether this arrest and the use of this type of restraint was necessary in the circumstances," she said. "We have met with the man involved and we will be keeping him and all interested parties updated throughout the investigation."

Anyone who witnessed the incident, or has footage which may assist the investigation, should email witness@ipcc.gsi.gov.uk or call 0800 151 0020.