The mobile video was shot inside a police station in Badaun in western UP on Monday. The target of the caning and humiliation was a young leader of the Samajwadi Party, which lost power in the state recently. His offence was to be involved in a fight between two groups over a bus ride.
In the video, Mr Singh first explains to a constable how to hold the man down for the thrashing. He suddenly yanks down the constable, who bends but appears uncertain about whether the demo by his boss includes a beating.
The constable then grabs the politician, Swaley Chaudhary, and holds him tight.
Mr Chaudhary was arrested along with 12 others after a brawl at the local bus station over boarding a bus. Two groups were fighting over who would board the bus first. An argument led to clashes in which even sticks and stones were used. There was firing too, according to the police.
"The inspector caned this person inside a police station and this is totally unacceptable. No one, including the police, has the right to violate human rights," said Chandra Prakash, Badaun's police chief.