The former head of security at Rupert Murdoch's UK newspaper empire has threatened to blow the whistle with "shock" revelations about the company.

Mark Hanna, who was cleared of perverting the course of justice in the phone hacking trial last year, spoke out after it was confirmed that Rebekah Brooks was returning to News UK - formerly News International.

It was announced on Wednesday that Mrs Brooks, 47, had been appointed to her former role as chief executive, a year after she was also acquitted of all charges in the high-profile trial.

In a video posted on YouTube Mr Hanna, who left his job in January, said: "To me - as previous director of group security - this is Murdoch's middle finger being shoved right in my face after standing trial with her and others, in what was classed as the trial of the century.

"I'm now standing up to all those who sit back and treat us with contempt, the Murdochs and Brooks of the world."

Mrs Brooks quit as chief executive of News International, publisher of The Sun, The Times and Sunday Times newspapers, at the height of the phone hacking scandal in July 2011. She reportedly walked away with a payout of more than £10 million.

Mr Hanna - a former soldier who had been employed at News International since 2009 - was reported to have received £30,000 after he was made redundant.

He has since said he has been unable to find other work because of the "stigma" of being involved in the phone-hacking trial.

Mrs Brooks was acquitted of being part of the hacking conspiracy, along with former News of the World managing editor Stuart Kuttner, following a 138-day trial which ended in June last year.

Her husband Charlie Brooks, her former PA Cheryl Carter and Mr Hanna were also found not guilty of perverting the course of justice.

Former News of the World editor Andy Coulson, who went on to become David Cameron's director of communications, was convicted and handed an 18-month prison sentence.

Meanwhile, the newspaper's former journalists Greg Miskiw, Neville Thurlbeck, James Weatherup and Ian Edmondson pleaded guilty to their role in the hacking, along with private detective Glenn Mulcaire.

It has since emerged that the company could face corporate criminal charges over phone hacking.

The Crown Prosecution Service said last week that the Metropolitan Police had handed over a "full file" of evidence relating to hacking at the News of the World.

Following her appointment, Mrs Brooks said: "I am delighted to return to News UK. It is a privilege to be back amongst the most talented journalists and executives in the business.

"I am confident that we can meet the many challenges of this digital age with a combination of cutting edge technologies and world class journalism."

A spokesman for News UK said: "Mark Hanna has been through an exceptionally difficult time.

"He was acquitted in court and, throughout the trial, we supported him and paid his substantial legal fees. We also continued to pay his salary and bonuses and provided other financial support throughout his trial and afterwards. When he said he wished to return, we offered him a comparable position with the company.

"Despite all our efforts to find a resolution with Mark, the matter is now before an employment tribunal, a fair and independent proceeding, where the company will defend itself vigorously. We consider his YouTube video to be an attempt to force News UK into offering an unreasonable financial settlement.

"Of course, we completely reject his accusations of illegal conduct."