The police watchdog is investigating after a student protester was left with bleeding on the brain after being hit with a police truncheon.
Alfie Meadows, a philosophy student at Middlesex University, was struck as he tried to leave the area outside Westminster Abbey during Thursday's tuition fee protests, his mother said.
The Independent Police Complaints Commission has launched an investigation, but said inquiries were still at an early stage.
After falling unconscious on the way to Chelsea and Westminster Hospital, Mr Meadows underwent a three-hour operation for bleeding on the brain.
His mother Susan, 55, an English literature lecturer at Roehampton University, said: "He was hit on the head by a police truncheon. He said it was the hugest blow he ever felt in his life.
"The surface wound wasn't very big but, three hours after the blow, he suffered bleeding to the brain. He survived the operation and he's in the recovery room."
Mr Meadows was with a number of friends, including two lecturers, Nina Power, a colleague of his mother's, and Peter Hallward, a philosophy lecturer at Kingston University.
But as they tried to leave the area where protesters were being held in a police "kettling" operation, the second-year undergraduate suffered a blow to the head.
His mother, who stayed up all night in the hospital with her son, said he was taken to hospital after his condition deteriorated.
Speaking later, Mrs Meadows added: "The wonderful news is that Alfie is talking and doing very well. But he's got tubes coming out of him everywhere. He will be in hospital for quite a while, it was a very major thing.
"He can remember the demonstration. He wanted to know whether other people were hurt, what happened afterwards and whether his friends were OK. We're just absolutely unbelievably thrilled that he has come through it. It was the most tremendous blow to his head.
"Basically he had a stroke last night. He couldn't speak or move his hand. But thanks to the wonderful medical care he's come through it. It was terrifying."