They added, "The 22-year-old man was arrested at approximately 02:00hrs on Wednesday, 10 July by officers from the Met's Royalty and Specialist Protection Command after he climbed over the front gates at Buckingham Palace".
Scotland Yard said the man was not carrying weapons and the incident was not terror-related, according to The Guardian.
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.
The Sun reports that a 22-year-old man actually scaled the Buckingham Palace fence around 2 a.m., and attempted to enter through various doors by banging on them throughout the property for nearly five minutes before help arrived.
She was reportedly the only senior royal sleeping in the household at the time.
Past year a homeless man who trespassed in the grounds of Buckingham Palace and damaged items before sleeping on them was jailed for 28 days.
The breach came almost 37 years after Buckingham Palace's most well-known security incident, when 30-year-old Michael Fagan gained access to the queen's bedroom while she was there. "The intruder was immediately arrested and didn't manage to get near the main building".
"He remains in custody at a central London police station".
The source says the intruder was detained under the mental health act. What about heat censors and CCTV? "It's very unusual given the infamous Fagan business almost 37 years ago", the source says.
In a 1993 BBC interview, Fagan highlighted the lack of security saying: "I don't know how the hell I found her [the Queen]".
"He was determined to get inside the palace and was banging down the doors but, thank goodness, this time everything was locked up".
The palace spokeswoman declined to say whether the Queen had been informed of the incident.
The 31-year-old schizophrenic then began talking to her about his family problems.
"The man was able to scale the very large metal fences outside the palace".