Two youths have been questioned by police on suspicion of trespass at the Palace of Westmisnter.
Police attended reports of two boys climbing over the low barriers into a car park at the southern end of Parliament grounds over the weekend.
Two 15-year-olds have been arrested and have since been bailed pending further enquiries.
The incident happened just 10 days after four people were killed in the horrific Westminster terror attack that shook the capital.
The Metropolitan Police said the trespass lasted around 30 seconds before the pair crossed back over into the public area when officers approached them.
They attempted to flee the scene but were pursued and detained by police.
The intruders did not gain access to any building, the police added.
Two boys were arrested on suspicion of trespassing on a protected site, contrary to section 128 of the Serious Organised Crime Act 2005, shortly before 2.30pm on Saturday (April 1).
Both the arrested youths were taken into custody at a central London police station.
The following day they were bailed, pending further enquiries, to return to a central London police station on a date in early May.
This incident is not being treated as terrorist-related.
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