LONDON (REUTERS) - Rebekah Brooks, the former head of Rupert Murdoch's British newspaper arm, asked for her office to be swept for listening devices the day before police reopened their investigation into phone-hacking, a London court heard on Monday.

The Old Bailey was also told that Murdoch's News International set up three security operations, nicknamed Blackhawk, Kestrel and Sparrowhawk, to protect executives when they were sent threatening letters at the height of public anger in 2011 over phone-hacking allegations.

"Can we have my phones, and office swept ... thanks. Discreetly," Brooks wrote in an email to Will Lewis, a senior News International executive, and Mark Hanna who ran the company's security operation.

The email was sent on Jan 25 2011, the day before London's Metropolitan Police announced a new investigation into hacking by journalists at Murdoch's News of the World tabloid.

Brooks, a former editor of the News of the World and News International chief executive from 2009, denies charges of conspiring to hack phones, authorising illegal payments to public officials and conspiracy to pervert the course of justice by hiding material from police.

Lawyer William Clegg, representing Hanna who is accused of helping Brooks to conceal items from detectives, told the court office sweeps were "entirely normal and routine", and were regularly carried out at newspaper buildings to ensure rivals could not find out about exclusive stories.

He also said there had been daily sweeps carried out in 2011 because Murdoch's News Corp was at the time in the process of trying to buy full control of British pay TV operator BSkyB, a plan which was ditched in the wake of the phone-hacking furore.

Cross-examining Jane Viner, the operations manager for News International, now known as News UK, Clegg said the scandal had led to members of the public sending threatening and abusive letters to Brooks and other company executives, so much so that mail was being monitored by the security team.

"I do remember Mark (Hanna) talking to myself and others about it," Viner said, agreeing that the perceived security risk had never been higher.

Clegg said police later found a large volume of threatening letters at Hanna's home.

As a result, News International brought in an external firm, International Corporate Protection, to bolster security. They organised three operations to provide bodyguards for Brooks, Lewis and public relations executive Simon Greenberg, the jury were told.

This led to a 24-hour physical presence outside Brooks's home in Oxfordshire and her flat in London.

Earlier the court was told that on July 14, 2011, the day before she resigned from News International, Brooks had been making plans to move her office from the firm's London headquarters to her Oxfordshire home.

Brooks, Hanna and five others deny all charges and the trial continues.