A man has been arrested on suspicion of attempted murder in connection with a student protest in London last week.
Hampshire Police arrested the 18-year-old, from the Hythe area of Southampton, on Monday before he was taken to London for questioning.
A fire extinguisher was thrown from a roof at the Conservative Party headquarters when violence erupted during a protest over tuition fees.
A 23-year-old student arrested on Friday was released on bail.
The man, who comes from Reading and studies at Anglia Ruskin University, in Cambridge, was questioned on suspicion of violent disorder.
More than 50 arrests have been made since the demonstration last Wednesday which saw a group of protesters surge into the Tory base at Millbank Tower in Westminster, central London.
Windows were smashed, fires lit and missiles hurled at police after protesters reached the building's roof.
Senior police officers said the extinguisher narrowly missed injuring two territorial support group officers, brushing down the back of one and hitting the knees of another.
Thousands of people had been demonstrating against plans to cut higher education funding and teaching grants.