The 22-year-old is currently in custody at a central London police station
The 22-year-old from Croydon was spotted by police officers who were monitoring CCTV early this morning.
The man was arrested on suspicion of trespassing on a protected site at about 4:15am this morning.
Met Police said in a statement that the man had been drinking and was not armed.
The man is currently in custody at a central London police station and police say the breach is not believed to be terrorism related.
The Queen of England is currently at Balmoral in Scotland and it is understood that no members of the Royal Family were in residence at the time of the arrest.
Buckingham Palace declined to comment on the incident.
Additional reporting by IRN