Officers met the man as he dropped to the ground and arrested him for trespassing on a designated site, Scotland Yard said.
Scotland Yard said: `A man has been arrested after climbing a gate at Buckingham Palace.
`Shortly before 1.45pm today police at Buckingham Palace were alerted to a man climbing over the south gate.
`As he dropped to the ground he was met by officers and arrested for trespassing on designated site, contrary to Section 128 Serious Organised Crime and Police Act 2005.
`He was not found in possession of any offensive weapons.
`The 21-year-old man was taken into custody and will undergo a mental health assessment. Enquiries by officers continue.`
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