Police have arrested an 18-year-old on suspicion of attempted murder after a fire extinguisher was thrown at officers during the Millbank riot.
Scotland Yard said the man was detained by Hampshire Police in Southampton on Monday.
He is travelling to London where he will be questioned by officers from the Metropolitan Police.
On Friday, a 23-year-old, a student at Anglia Ruskin University in Cambridge, was arrested and then released on bail on suspicion of violent disorder.
A Met spokesman said: “This arrest follows an investigation into public disorder where a fire extinguisher was thrown from the roof of Millbank Tower.”
Police Federation representatives have called for the person who flung the empty metal fire extinguisher to be charged with attempted murder.
Senior officers said it narrowly missed injuring two territorial support group officers, brushing down the back of one and hitting the knees of another.
The incident was one of the defining moments of the four-hour stand-off last week after a breakaway group of students attacked the Millbank office complex.
Up to 50 demonstrators smashed windows, discharged fire extinguishers and threw debris from the roof of the building. But hundreds of others gathered in a forecourt below booed the culprit and shouted to others to stop damaging the building and throwing missiles.
The Met said 10 of the 54 people arrested during sprawling outbreaks of disorder were under the age of 18.