Police used CS spray on protesters at an anti-tax avoidance demo yesterday after an activist was arrested while pushing leaflets into an outlet of Boots.
Officers detained the woman on suspicion of causing criminal damage during a sit-in demonstration at the store in Oxford Street, central London.
Demonstrators said she simply bent the rubber seal between the doors of the premises as she attempted to push leaflets through.
As officers arrested her, a confrontation took place during which a member of the police used a CS spray.
Three people were taken to hospital for treatment following the incident, London Ambulance Service said.
Scotland Yard confirmed that CS spray had been used to disperse protesters during the arrest, which took place shortly after 2.30pm.
After the incident, nearby shop Ben's Cookies handed out milk for those affected to douse their eyes with and activists from campaign group Uncut added that staff from Boots – the focus of the demo – gave them free eye wash.
Uncut accuses the retailer of cheating the UK out of huge sums of cash as a result of being registered in Switzerland, where taxes are far lower.
It had organised a co-ordinated day of action across the UK, with demonstrators focused on outlets of Boots and supermarket chain Tesco.
Around 20 activists dressed in surgical masks and bloody bandages were escorted out of a branch of Boots in Oxford Street at around 1pm and the store shut its doors. But around an hour into the sit-down protest, police moved in to arrest a female demonstrator.
One of those affected, Jack Winstanley, 26: "I didn't know what was happening, it happened quickly and it has never happened before to me.
"Then my eyes were burning, my face was burning."
A spokesman for Scotland Yard said: "A female was arrested on suspicion of criminal damage. CS spray was deployed in the incident."
CS spray is carried by officers as a matter of routine, the Metropolitan Police spokesman said, adding that there was no lasting damage to people affected.
At a related protest in Lewes, East Sussex, five people were arrested as protesters blocked the entrance to the county town's branch of Boots.