The man’s family have accused a police officer of tackling the eight-stone father to the ground after he made a gesture at them, “repeatedly punching him in his face”.
The family claim the other two officers said their backs were turned and did not see the punches.
The Metropolitan Police said a “struggle ensued” when the man got out of the car and say their officer suffered an injured eye during the arrest at midday in Blyth Road, Bromley on Monday.
They added they had given first aid to the man before arresting him on suspicion of assaulting an emergency worker.
“My dad is born and bred Jamaican whose accent is very strong and isn’t afraid to say what he feels about the Met Police and their corrupt racist system.
“My dad made hand gestures telling them to leave him alone they felt it was now their duty to physically abuse him.“
“My dad is 70 years old, no more than 8 stone, 5ft 6 who has had multiple strokes, heart problems and is also on blood thinning tablets.
“Multiple witnesses have stepped forward to describe the absolute torture they put my dad through until my brother turned up.
“My dad has suffered a broken nose, broken cheek bone/ eye socket and deep cuts to his head and other injuries.
“I’m absolutely heartbroken.”
In another post, she addressed the officer directly: “Honestly do you know the excessive force it takes to break someone’s nose and shatter their eye socket.
“Mr officer you was moving like you wanted to give him brain damage, blind him or even kill him.
“Was it really needed sir?”
A Metropolitan Police spokesman said the force was aware of the Instagram post.
He added: “After exiting the vehicle, the driver became involved in a struggle with an officer during which the officer sustained an injury to his eye.
“The driver, a 70-year-old man, was arrested on suspicion of assaulting an emergency worker.
“He sustained a facial injury during the struggle and was given first aid by officers before being transported to a south London hospital.
“He was later discharged from hospital before being taken to a police station from where he was released under investigation.”
The arrest has been referred to the Independent Office for Police Conduct.