The man did not gain access to the palace

The 27-year-old was arrested in the early hours of Wednesday morning but a police spokeswoman said he did not get close to the palace.

Police said they had responded to an alert triggered by an alarm system within the palace grounds at 0200 GMT.

The man was arrested at a perimeter wall and taken to Belgravia Police Station for questioning.

He was released on bail on Wednesday night to return on a date in February.

A woman in the Mall was also detained for questioning but not arrested.

The incident is not thought to be terrorist-related.

False reference

The security breach comes after Daily Mirror reporter Ryan Parry exposed flaws in royal security last month by gaining a job as a footman at Buckingham Palace using a false reference.

Mr Parry worked for two months at the Palace despite unprecedented security in advance of the visit of US President George Bush.

Barschak mingled with royal guests

And in June self-styled "comedy terrorist" Aaron Barschak, dressed as terrorist leader Osama bin Laden in a pink ball gown, gatecrashed Prince William's 21st birthday party.

Home Secretary David Blunkett announced a "thorough review" of Buckingham Palace security following the Daily Mirror incident.