Rupert Murdoch was last night preparing to fly to Britain to join frantic efforts to secure the future of The Sun after the arrests of five senior journalists by police investigating allegations of bribery and phone hacking.

Police swooped on eight individuals between 6am and 8am yesterday, arresting the five Sun journalists, two Ministry of Defence staff and a police officer. The arrests came hard on the heels of five related arrests two weeks ago when four senior Sun journalists and a police officer were questioned in connection with bribery allegations. All eight were released on bail last night.

The latest astonishing development, which came two days after the Leveson inquiry into press standards finished its first session, prompted fury among the newspaper's staff, amid allegations that those arrested had been "thrown to the wolves" in an effort to bolster the embattled News Corp empire, and, particularly, to rekindle its hopes of taking over BSkyB. The police were acting on information provided by News International, owner of The Sun and Times newspapers, through its Management and Standards Committee (MSC).

Amid fury among the paper's editorial staff, Mr Murdoch was forced to issue a pledge last night that he was not preparing to sell the newspaper, via his chief executive, Tom Mockridge. Senior staff were told that Mr Murdoch planned to fly to London to calm the situation. Journalists including the paper's deputy editor were bailed after being questioned in connection with allegations of making illegal payments to police officers and other officials.

The investigation broke new ground yesterday: for the first time, the arrests broadened beyond payments to police, with a female member of the MoD and a member of the armed forces also held while their homes were searched following dawn swoops by officers working on the Elveden investigation. The journalists arrested were Geoff Webster, The Sun's deputy editor; John Kay, a former chief reporter who joined the title in 1974; Nick Parker, chief foreign correspondent; John Edwards, picture editor; and John Sturgis, a reporter. The paper's editor, Dominic Mohan, said: "I'm as shocked as anyone by today's arrests but am determined to lead The Sun through these difficult times.

"I have a brilliant staff and we have a duty to serve our readers and will continue to do that. Our focus is on putting out Monday's newspaper."

Nevertheless, there were fears that the worsening crisis at the red-top, sister paper of the now defunct News of the World, could have wider ramifications for the Murdoch media empire, as the Leveson inquiry prepares to examine the relationship between journalists and police. In 2003, The Sun's former editor Rebekah Brooks admitted to a parliamentary select committee that her journalists paid police officers for information, which is illegal.

Sources suggested that Mr Murdoch was being sent texts and emails from irate staff at the newspaper. Michael Wolff, Mr Murdoch's biographer, who has inside knowledge of News Corp, said last night that the latest arrests put pressure on theproprietor to close The Sun: "I've never known a point in News Corp history with so much internal acrimony... Murdoch must feel this is so out of control. He faces his son's arrest, a Department of Justice investigation, more bribe revelations, more hacking fallout and challenge to BSkyB control."

Yesterday's arrests mark the latest controversy surrounding the MSC, which has provoked anger among journalists at NI's Wapping offices. Several have protested strongly, warning that morale has been undermined. The latest criticism came from the National Union of Journalists, which accused Mr Murdoch of throwing his journalists to the wolves in an effort to save his company, adding that the reputation of those arrested will "inevitably" be damaged. The union's general secretary, Michelle Stanistreet, said News International staff were furious at "what many sense to be a witch hunt" and "a monumental betrayal on the part of News International". "Once again Rupert Murdoch is trying to pin the blame on individual journalists, hoping that a few scalps will salvage his corporate reputation," she said.

There were suggestions in Wapping that the MSC was, to quote one source, "draining the swamp" in an attempt to revive the BSkyB deal that fell apart last year in the wake of the phone-hacking scandal at the News of the World. Yesterday's arrests are the clearest indication yet that illegal activity was not limited to the News of the World, as was initially thought.

NI's chief executive, Tom Mockridge, sent a memo to staff at The Sun yesterday, giving them his "personal assurance" from Mr Murdoch that he plans to continue to own and publish The Sun. Speculation has been mounting since the closure of the NOTW last summer that Mr Murdoch might sell his three remaining British national newspapers. Some Wall Street analysts have said that selling these newspapers could add as much as 20 per cent to the News Corp share price.

Mr Mockridge's memo sought to reassure staff at The Sun and to stand by those arrested. "This news is difficult for everyone on The Sun and particularly for those of you who work closely with those involved. Some of the individuals arrested have been instrumental in breaking important stories about public bodies, for example the scandal of our underresourced troops in Iraq," he said.

"We must take care not to pre-judge the outcome of the police interviews." News International has provided legal support to those interviewed by police today.

Tom Watson, the Labour MP who has been instrumental in exposing the extent of illegal activity at News International, welcomed the arrests and in a letter to Mr Mockridge called for the issues that led to Rebekah Brooks's resignation to be re-examined. "It seems that Mr Rupert Murdoch now understands the seriousness of the situation News Corp in the UK finds itself in. Under your leadership, the Management and Standards Committee is, for the first time, ensuring that News Corp UK is fully co-operating with the police investigation into wrongdoing at News International. Clearly, allegations of illegal payments to police officers are more serious offences than those of phone hacking."

Yesterday's dramatic developments are the second batch of high-profile arrests at The Sun to take place in two weeks.