Police have been accused of trying to stop civilians injured during the student protests being treated at the same hospital as officers.
Protester Alfie Meadows, 20, needed brain surgery after allegedly being hit with a police baton.
His mother Susan Matthews said police objected to him being treated at Chelsea and Westminster Hospital.
She told BBC London his ambulance driver was angry about the stance. The police have refused to discuss details.
They said because the incident was under investigation by the Independent Police Complaints Commission (IPCC) they were unable to discuss it.
A Met spokesman added: "The London Ambulance Service is part of our planning process for major events and agreements are made in advance about these matters.
"However, it remains the decision of the LAS where patients are taken on the day based on a number of factors."
An IPCC spokesman said if a complaint was made about the issue it would look into it.
A spokesman for Chelsea and Westminster Hospital confirmed a decision had been taken to treat officers there and civilians in other hospitals.
But he said because so many protesters ended up being injured some were treated at the hospital.
He denied that any civilians were turned away.
Mr Meadows, a philosophy student, suffered bleeding on the brain.
When he arrived at Chelsea and Westminster Hospital there was a "stand-off" between police and medical staff in a corridor over where he was treated, Ms Matthews said.
The student was initially treated at Chelsea and Westminster, but was transferred to Charing Cross Hospital where there is a specialist brain injuries unit.
He is said to be recovering.