A 24-year-old man has been arrested on suspicion of trespass at Buckingham Palace.
Police said the man had stepped over a low perimeter fence and was trying to climb an outer wall on Sunday evening.
He was not found to be carrying a weapon and the incident is not being treated as terrorist related. He has been released on conditional bail.
He was also held on suspicion of being in possession of a controlled substance but faces no further action over this.