A lone policewoman struggled to apprehend a suspect she thought could be carrying drugs before back-up arrived and discovered a foot-long knife behind a nearby wall.

The policewoman followed the brazen 21 year old as he tried to walk away on the street in Brixton, south London, and avoid arrest.

The officer, who stands at just four-and-half-feet tall, tried to apprehend the suspect for three minutes and followed him along Acre Lane on her own.

Officers who arrived as back-up then discovered a foot-long knife behind a nearby wall.

The suspect was arrested on suspicion of possession of an offensive weapon in a public place and obstruction of a drug search.

Shocking footage filmed in Brixton, south London, shows the policewoman powerless to stop the suspect from walking away

The incident happened at 1.20pm when the female officer noticed a man acting suspiciously in Windrush Square, the Met police confirmed.

She approached and stopped him on Acre Lane under the Misuse of Drugs Act. The man resisted arrest and repeatedly tried to get away from the officer.

As the man tried to make his escape he was caught on camera by a passerby, who wishes to remain anonymous.

The 25 year old from Croydon who filmed the incident told MailOnline that he was too apprehensive to intervene but took his phone out and followed the pair 'in case anything happened to the woman'.

He began recording on Brixton Road outside a branch of McDonald's.

The officer followed the man, who is 6ft tall and wearing a tracksuit, and repeatedly tried to handcuff him but he shrugged her off and carried on walking.

A knife (pictured) was found just feet away from where the suspect was arrested on Acre Lane in Brixton

At one stage a man wearing a motorcycle helmet did step in and try to assist the officer, but shortly afterward back-up arrived. These officers found a knife on the ground.

The man filming said that the knife had been pointed out as being behind the wall by a person nearby just as the arrest was being made.

He added: 'The video doesn't do it justice... It was about a foot long.'

The man was arrested, taken to a south London police station and eventually released under investigation.

The cameraman told MailOnline: 'I always see lone policewomen and unfit policemen patrolling our streets that don't look able to give chase or have the physical power to make an arrest.

'She was saying: "Please sir, stop," over and over to him but he kept flinging her off. She was being polite with him.'

A man in a motorcycle helmet tries to help the policewoman who is grappling with the suspect

Back-up arrives in a police van and the young man is apprehended

He added that he recorded the footage, 'to prove a point' to his colleague.

'My colleague was apprehensive about following them because he thought 'he probably has a knife on him' but I carried on regardless.'

'But physically, she had no chance,' he added.

'She was four-and-a-half foot. This six-foot guy was pushing her around. It's just not effective, really.'