Security has been tightened since a 2003 newspaper expose

Robert Stansfield, 25, was detained on Friday evening after a job interview for the Royal Household, and has been released on bail until March.

The Mirror said he had been "engaged in a legitimate journalistic enterprise", testing staff recruitment procedures.

Palace security was overhauled after another Mirror reporter, Ryan Parry, got a job as a palace footman in 2003.

We're pleased to see that the palace has learned the lessons of our previous investigation Mirror Group spokeswoman Intrusions over the years

Parry worked for two months in the palace after using a false reference to get the job.

That tabloid breach prompted Buckingham Palace to review security and appoint a new director of security, Brigadier Jeffrey Cook.

Following Stansfield's arrest, a Mirror spokeswoman said: "Following the paper's 2003 expose of security surrounding the Royal Family, [the reporter] was instructed to test the robustness of current procedures for staff recruitment by applying for a job as a member of the household.

"We're pleased to see that the palace has learned the lessons of our previous investigation and since tightened its security procedures."

A Buckingham Palace spokeswoman said it did not comment on security matters.

Police checks

A Scotland Yard spokeswoman confirmed a 25-year-old reporter had been arrested on Friday at the palace and questioned at a central London police station.

He was arrested on suspicion of attempting to obtain pecuniary advantage, theft and false accounting.

Windsor Castle was breached at Prince William's 21st birthday

Checks on his application by SO14, the Met branch which helps vet royal staff, had revealed some false details, according to the spokeswoman.

Last month, a News of the World reporter was arrested in similar circumstances and is now on bail.

Bethany Usher had been investigating palace security in what the paper called a "legitimate journalistic exercise".

Police investigating that incident also arrested a 33-year-old man, not believed to be a reporter, who has been bailed.

According to the Independent Security Commission, the most likely threat of infiltration of the Royal Family came from journalists and others wishing to "test" security measures or to cause embarrassment.