Secret CCTV footage has uncovered the horrific physical abuse and verbal torment a mental health patient suffered at the hands of six policemen on the front lawn of his home.

Disability pensioner John had locked himself inside his Melbourne property when his psychologist called emergency services in October last year - concerned the man could self-harm.

When police arrived, he told them he was vomiting blood and had diarrhoea - nasty side effects he claimed were a result of withdrawing from medication for his back pain.

But an altercation at his door step sparked a horrific 20-minute episode that would see him held down by six officers, brutally beaten with a baton, verbally abused and capsicum sprayed in the face.

Secret CCTV footage has uncovered the horrific physical abuse and verbal torment a mental health patient suffered at the hands of six policemen on the front lawn of his home

'You f***ing idiot... You like that? Smells good doesn't,' one officer said in the footage, obtained by Fairfax Media.

'Get your f***ing hands behind your f***ing back,' he continued as John screamed in agony after receiving six blows to the leg from a baton.

'Oh God my back... My eyes... You happy? How tough are youse?' he asked.

In a final humiliation, John was sprayed with a high-pressure hose as he sat handcuffed and in tears on his lawn.

A grinning policeman pulled out his phone to film the ordeal - and appeared to ask his colleague to continue hosing John so he could capture it on camera.

An altercation on John's door step sparked a horrific episode that would see him held down by six officers, brutally beaten with a baton, verbally abused and capsicum sprayed in the face

'You f***ing idiot... You like that? Smells good doesn't,' one officer said in the footage

'It was like a game for them. They wanted to get their rocks off, you know? It's wrong,' John told the ABC's 7.30.

'He's aiming for my nostrils and it's going into my lungs - and that's when I started choking from the water and from the hot mace going into my respiratory [system].

'I couldn't breathe. I really, literally, thought I was going to drown. You can feel the mace and the water together in your lungs.'

Victoria Police issued a statement on Tuesday morning, saying it had 'no tolerance for poor behaviour within its ranks'.

In a final humiliation, John was sprayed with a high-pressure hose as he sat handcuffed and in tears on his lawn, while a grinning officer filmed the ordeal

Victoria Police issued a statement on Tuesday morning, saying it had 'no tolerance for poor behaviour within its ranks'

'We want people to have absolute confidence that when they make a complaint against police it will be investigated thoroughly and with integrity,' the statement read.

'We will examine carefully any new evidence contained in today’s media reports. If matters need to be revisited, then that is what will occur.'

The case is now in the hands of Victoria's public sector watchdog, the Independent Broad-based Anti-corruption Commission.