A man has been arrested on suspicion of being an illegal immigrant after he scaled the fence around Buckingham Palace, police have said.
Officers immediately stopped the intruder in the palace forecourt
The intruder, in his 30s, got into the palace forecourt on Saturday afternoon before officers stopped him. The Queen is not thought to have been there.
Scotland Yard said the man was now at a central London police station.
"He was arrested on suspicion of illegal entry into the UK and so we are liaising with the immigration service."
The arrest is the latest in a string of security breaches involving the Royal Family in the last few years.
Last September, Fathers 4 Justice campaigner Jason Hatch scaled the palace walls to protest about access to his children.
The then Metropolitan Police chief, Sir John Stevens, said officers responded within 18 seconds but admitted that questions remained about palace security.
One of the most famous breaches of security was in 1982 when 31-year-old Michael Fagan broke in and spent ten minutes talking to the Queen in her bedroom.
Buckingham Palace security breaches
1982 - Michael Fagan enters Queen's bedroom
89 - mentally-ill Michael Crook walks past armed guards
90 - Two separate break-ins, one intruder claims Queen is his 'mum'
91 - Man gets within yards of Queen's private apartments
92 - Kevin McMahon arrested inside grounds twice in a week
94 - Naked paraglider lands on palace roof
95 - Student John Gillard rams gates with car
97 - Absconded mental patient wanders grounds
03 - Mirror writer Ryan Parry gets job as footman
04 - Fathers 4 Justice protester climbs wall of palace
He had scaled the walls around the palace and clambered up the drain-pipe to the Queen's private apartments.
The barefooted father of four evaded electronic alarms and palace and police guards before disturbing the Queen by opening a curtain.
In 2003, two incidents led to the appointment of a new Royal security co-ordinator.
A comedian gatecrashed Prince William's 21st party at Windsor Castle in June and a reporter got a job as a footman a few months later.
Aaron Barschak's stunt led to a review of security after a report criticised the way police handled the party.
Aaron Barschak sparked a major review of security
The report - by Commander Frank Armstrong of the City of London police force - gave 28 recommendations for changes to the way the Royal Family was protected.
They included changes to police control room procedures, better communication between agencies and regular checks of alarms and CCTV cameras.
A new law to make trespassing on royal property a specific crime to act as an extra deterrent was also recommended.
But just three months later, Daily Mirror journalist Ryan Parry managed to get a job as a palace footman using false references.
Mr Parry responded to a job advertisement on a recruitment page of the Buckingham Palace official website.
On his CV, he left out any mention of his journalistic career and included one fake reference and one real one.
Another review focused on tighter vetting, including examining what role MI5 might play.
Shortly afterwards, former SAS officer Brigadier Jeffrey Cook took up the role of Palace Director of Security Liaison.
That led to new vetting procedures for staff being put in place to examine family background, financial statements, credit card debts and references.
Since then, the palace has stepped up its efforts to increase security, particularly for the opening of the palace to the public in the wake of the 7 July London bombings.