Two 15-year-old boys managed to climb over the barriers into the grounds of the Palace of Westminster just days after a terror attack prompted questions over security at Parliament.
The boys were chased by police after they were spotted scaling a low barrier into the car park at the southern end of the Palace, before crossing back into the public area when they were seen by nearby officers.
The alleged trespassers were arrested and bailed, the Metropolitan Police said. The pair are not said to have gained access to any part of the building.
The incident lasted approximately 30 seconds.
The incident took place on Saturday, just 10 days after a deadly attack by Adrian Ajao, also known as Khalid Masood, who took the lives of four people, when he drove his car into crowds and stabbed a policeman outside the Houses of Parliament.
The attacker was shot dead by armed police after fatally wounding police constable Keith Palmer, who was stationed at the Palace's western border.
Grave concerns over security measures at the site of Parliament were raised in the wake of the attack.
Both youths were held at a central London police station and bailed on Sunday April 2, pending further inquiries in May.
The incident is not being treated as terrorist-related, the Met said.