LONDON — After barely a year as Britain's prime minister, David Cameron is facing the gravest crisis of his political career, forced onto the defensive by a spiraling phone-hacking scandal that has sown turmoil inside the media, Scotland Yard and the hallowed halls of 10 Downing Street.
Cameron came under increasingly heavy fire Monday for appointing a one-time tabloid editor as his top communications aide, bringing into his inner circle a man now suspected of conspiring to hack into people's cellphones and of bribing police officers for information.
The former aide, Andy Coulson, who resigned as the government's communications director in January, was arrested last week.
Cameron has struggled to rebut accusations that he displayed alarmingly poor judgment in hiring Coulson over the reservations of other senior politicians and that he cultivated unhealthily close ties with executives working for media mogul Rupert Murdoch.
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"He was warned and warned about Andy Coulson," said Jonathan Tonge, a politics professor at the University of Liverpool. "This is Cameron's first crisis for which he is solely accountable."
Records also show that, since becoming prime minister, Cameron has met with executives of News International, the British division of Murdoch's giant News Corp., almost once every two weeks on average — far more than with executives from any other news organization.
Compounding the damage, the head of Scotland Yard — Britain's most senior police official — quit over the hacking scandal Sunday. On Monday, the police department's top counterterrorism officer also stepped down.
The growing concern over Cameron's leadership forced him to cut short a trip to Africa this week. At a news conference Monday in South Africa, he said he would address the hacking scandal in an emergency session of Parliament on Wednesday, when lawmakers were originally supposed to start their summer recess.
Cameron's reputation has been badly stained by the furor and by the doubt cast on his personal judgment, analysts say.
"It has damaged him," said Steven Fielding, a political science professor at the University of Nottingham. "It opens a gate that was hitherto shut on David Cameron, because like him or not, he gave a very good appearance of being a very accomplished political performer. This now makes him vulnerable."
The allegations of widespread hacking of cellphones by the Murdoch-owned News of the World tabloid have triggered an avalanche of events that have left Cameron and his government hard-pressed to keep up.
The News of the World has been shut down. Two of its former editors, Coulson and Rebekah Brooks — both personal friends of the prime minister — have been arrested in the ongoing probe into the alleged hacking of phones belonging to celebrities, members of the royal household and crime victims.
Murdoch and his son James, once among the most powerful men in Britain because of their ownership of newspapers such as the Times of London and the Sun, are to give evidence today before Parliament.
On Monday, Scotland Yard Assistant Commissioner John Yates, under pressure for his ties to the News of the World and for declining to reopen an investigation into phone hacking despite thousands of pages of evidence, stepped down just as the police force's civilian oversight committee was preparing to suspend him. Yates' departure is a major setback as the force gears up for next year's massive security operation for the Summer Olympics.
In another twist, a former reporter at the News of the World who early on accused Coulson of knowing about phone-hacking at the paper apparently died at his home in Watford. Police said the death of a man British media identified as Sean Hoare was "unexplained, but not thought to be suspicious."
But it was the resignation of Yates' boss, Commissioner Paul Stephenson, that has sharply aggravated Cameron's woes.
Stephenson said he was stepping down partly because of the controversy surrounding Scotland Yard's hiring of a former News of the World deputy editor as a part-time public-relations consultant. Neil Wallis was hired in late 2009 even as the police were being pressed to revive their phone-hacking investigation into the News of the World after a lackluster first effort.
That original investigation had resulted in a News of the World reporter and a private investigator being convicted on hacking charges. Coulson, who was the paper's editor at the time, resigned over the incident in 2007.
Wallis, who had been Coulson's deputy, was arrested last week as part of a new probe into the hacking allegations. Stephenson said he was not aware of Wallis' potential involvement in the hacking scandal at the time of his yearlong contract with Scotland Yard.