Buckingham Palace said it was aware of the arrest

The woman was held on Thursday on suspicion of attempting to obtain pecuniary advantage, police said.

The specialist crime operations team was investigating and the 25-year-old was bailed until 9 February.

The News of the World said that its reporter Bethany Usher had been investigating palace security.

The paper described it as a "legitimate journalistic exercise".

False footman

Buckingham Palace said they were aware of the arrest on 19 January, but that it was a matter for the police.

Security at the palace was highlighted in 2003 when a Daily Mirror journalist managed to get a job as a footman in the months leading up to a visit by US president George Bush.

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

The tabloid breach prompted Buckingham Palace to review security and appoint a new director of security.

Brigadier Jeffrey Cook was appointed in May 2004 to oversee the co-ordination and royal protection and vetting of staff.

The Independent Security Commission said the most likely threat of infiltration of the Royal Family came from journalists and other people wanting to "test" security measures or to cause embarrassment.