Two men have been arrested and a security review launched following one of the most serious security breaches at the palace in decades.
The shocking break-in at Buckingham Palace sparked concerns after a man scaled a fence to get inside the Queen's home.
Police said the man was found "in an area currently open to the public during the day" and arrested for burglary, trespass and criminal damage.
A burglar broke into Buckingham Palace after climbing a wall and kicking open a door
A second man was arrested outside the palace for conspiracy to commit burglary following the incident on Monday.
A spokesman for the Metropolitan Police said both men have now been bailed.
"A review of the specific circumstances of this incident is being carried out. No members of the Royal Family were at Buckingham Palace at the time of the incident," they said.
Buckingham Palace has not yet commented on the incident.
The break-in is one of the most serious security breaches at the palace since 1982, when Michael Fagan evaded guards to get inside the Queen's private chambers while she was still in bed.
The unemployed father of four, 31, spent around 10 minutes talking to the Queen after he climbed over the palace walls and up a drainpipe.
The Queen managed to raise the alarm when Fagan asked for a cigarette, allowing her to call for a footman who held him until police arrived.
The Queen has been spending her summer break at Balmoral Castle since the beginning of August and is not expected to return to the palace until October.
She is expected to make her traditional appearance at a Highland Games today.
The security scare at Buckingham Palace is the latest in a series of incidents involving the Royal Family.
In March 2011 a car carrying the Prince of Wales and the Duchess of Cornwall was mobbed by demonstrators who had split from a protest against higher university tuition fees.
Camilla was visibly distressed after being poked in the ribs with a stick through an open window in the distinctive Rolls-Royce Phantom VI as she and Charles travelled to the Royal Variety Performance at the London Palladium.
In 2003, comedian Aaron Barschak managed to get into Prince William's 21st birthday party at Windsor Castle.
The self-styled 'comedy-terrorist' set off a series of alarms and was caught on CCTV before he joined 300 guests at the bash and was removed.