A man has been arrested after scaling the front gates at Buckingham Palace in the early hours of Wednesday morning.
The Metropolitan Police said officers arrested a 22-year-old man around 2am on suspicion of trespass.
The statement added that the man was apprehended by officers from the Met's royalty and specialist protection command after he climbed over the palace gates.
It continued: "The man was not found in possession of any offensive weapons and the incident is not being treated as terrorist-related.
"He remains in custody at a central London police station."
The Queen is likely to have been the only senior royal sleeping at the palace because there are renovation works being carried out.
The Duke of Edinburgh does not live at Buckingham Palace since retiring, but spends most of his time in Norfolk.
The police statement comes after The Sun reported an intruder was "on the loose" in the palace while the Queen slept.
However it is not known whether the man was arrested inside the building itself.
One source told the paper the intruder was "banging down the doors".
It has sparked concerns the intruder was attempting to copy a break-in by Michael Fagan, who was able to get into the Queen's bedroom 37 years ago.
He broke in on 9 July 1982 and was able to speak to the monarch for several minutes before her long-time aide came to her rescue.
Fagan was not charged, as at the time it was a civil wrong not a criminal offence, but he was charged with theft of half a bottle of wine which he had drunk on a previous incident in which he claimed to have entered the palace.
The charge was dropped and he spent six months in a psychiatric hospital.
Trespassing in Buckingham Palace became an offence in 2007.