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

Suspected criminals in London could soon have controversial 'spit guards' forced over their heads after the Met Police approved rolling out their use across the capital. Britain's largest force will reportedly introduce the technique for a pilot starting in October to protect officers from offenders who bite or spit at them.

The netted hoods have a guard over the mouth and have been criticised after claims they breach an individual's rights. Their use was brought into focus in July when footage emerged of police forcing one of the devices over a man's head during an arrest at London Bridge train station.

IK Aihie, 20, was detained at the station after arguing with his girlfriend and becoming aggressive toward officers. Video showed Aihie struggle as the hood is placed over his head in front of his distressed partner. The Independent Police Complaints Commission launched an investigation into the incident as a result of the video going viral on social media.

Critics say police treat potential offenders "like dogs" by bagging them in the hood but body armour supplier PPSS Group defended their use and said they protect prison and police officers, as well as paramedics from Hepatitis C and other infectious diseases.

"It is without question, we can effectively help protect frontline professionals by making Anti-Spit Masks available, " CEO Robert Kaiser said. "When confronted with a hostile or intoxicated member of the public, or disturbed hospital patient or inmate, the risk of being spat on is realistic and protection from such threat is sensible".

"Anti-Spit Masks are a compact, inexpensive and disposable device, already used by agencies and organisations around the world, such as law enforcement, correctional institutions, emergency medical services and state hospitals."

Speaking to the Guardian newspaper, Martha Spurrier, director of Liberty, said: "A spit hood is a primitive, cruel and degrading tool that inspires fear and anguish. We have seen many cases where the police use them unnecessarily and without justification, including on children and disabled people."