Image caption British tabloid the News of the World closed in July 2011 after 168 years in circulation

The row over phone-hacking by journalists has led to the closure of the News of the World newspaper, the establishment of the Leveson Inquiry, an MPs' inquiry and the launch of three police investigations.

The BBC takes a look at the key questions it poses.

What is the phone-hacking scandal?

The story goes back to 2006-07 when Clive Goodman, the then News of the World royal editor, and Glenn Mulcaire, a private investigator were convicted of intercepting voicemail messages left for royal aides and subsequently jailed.

Their newspaper said they had acted alone - but the then editor Andy Coulson quit, saying he took responsibility for what happened.

Two years later, the Guardian newspaper reported that News International had made confidential settlements totalling £1m to three people who said their phones had been hacked. By September 2010 a string of well-known people began legal moves to have their claims looked at again amid mounting suspicions that phone hacking had been more widely used.

The turning point came in January 2011 when the Metropolitan Police launched Operation Weeting, a fresh phone hacking investigation which included looking at the original 2006 case. The investigation slowly widened to include allegations of improper payments to public officials and separate claims of computer hacking.

The critical political moment in the affair came when the Guardian newspaper reported that the newspaper had hacked the mobile phone belonging to murdered schoolgirl Milly Dowler.

What happened to the News of the World?

The Sunday newspaper was one of the oldest in the UK and sold some 2.8m copies every week. Its fondness for sex scandals gained it the nickname "News of the Screws".

Rupert Murdoch closed it down in the wake of the Milly Dowler revelations. Its final front page declared "Thank you and goodbye".

Image caption Claims that Milly Dowler's phone was hacked were described as "truly dreadful" by the prime minister

How many people have been hacked?

More than 4,000 people have been identified by police as possible victims of phone hacking by the NoW. The forthcoming prosecutions (see below) specify 600 identifiable alleged victims.

The alleged targets have included politicians, celebrities, actors, sports people, relatives of dead UK soldiers and people who were caught up in the 7/7 London bombings.

How does phone hacking work?

The opportunity to access voicemail messages came down to a simple security oversight. Mobile phones used to be supplied with a default factory-set personal identification number that could be used to access voicemail from another phone or abroad. Customers were encouraged to change that Pin, but very few did.

That meant that anyone could call the phone and if the owner did not answer, the caller could use the Pin to access the voicemail and any stored messages.

Is phone hacking illegal?

Yes. Hacking voicemails is classed as an unlawful interception of communications under Section One of the Regulation of Investigatory Powers Act 2000.

Has anyone been charged?

On 24 July, the Crown Prosecution Service announced it would be charging eight people with phone hacking. The group includes Andy Coulson, the former News of the World editor and, more recently, David Cameron's former spokesman. Rebekah Brooks, the former chief executive of News International, was also among those charged. Both Ms Brooks and Mr Coulson have said they will fight to clear their names. Rebekah Brooks, her husband and others also face a separate charge of conspiracy to pervert the course of justice in relation to the police investigations.

What role has the Met Police played in the affair?

Image caption Sir Paul Stephenson quit as Met chief amid criticism for hiring an ex-NoW executive as an advisor

The Met has faced enormous criticism over its initial approach to the allegations.

The original inquiry in 2006 resulted in just two arrests. Officers told MPs on the Home Affairs Select Committee that News International had tried to "thwart" the original inquiry.

In 2009 the force decided not to relaunch the investigation despite pressure to do so. Since then, the force has faced claims of an overly cosy relationship with News of the World journalists. Sir Paul Stephenson quit as the Met's commissioner, as did assistant commissioner John Yates, following criticism of police links to former News of the World deputy editor Neil Wallis.

In February 2012, the force also formally accepted it had failed to warn some people they could have been victims of hacking by the NoW.

What has happened to victims?

News Corporation set up a special process to consider compensation claims for those who believe they were hacked. Some cases have already been settled in the High Court. These include a payment of £600,000 to singer Charlotte Church and her parents. You can read about more victims here.

How has the government handled the affair?

The prime minister has announced two inquiries and said the Press Complaints Commission should be scrapped.

Lord Justice Leveson is conducting a two-part inquiry, initially looking at "the culture, practices and ethics" of the UK press and its relationships with police and politicians. It will later examine the extent of unlawful conduct within newspaper groups and the police's original phone-hacking investigation.

Image caption Andy Coulson blamed coverage of the hacking story for his resignation

Former Parliamentary Commissioner for Standards Elizabeth Filkin has already examined the relationship between the media and Metropolitan Police.

She concluded that the "close relationship" between parts of Scotland Yard and the media had caused "serious harm". She said there were "some very serious issues" relating to contact between journalists and police which had "eroded trust from the public". Among her recommendations, she told officers to "watch out" for "late-night carousing" with journalists, and flirting.

Prime Minister David Cameron has faced questions over his judgement, given that he employed Mr Coulson.

How has News International responded to the scandal?

News Corp boss Rupert Murdoch has issued an apology for the "serious wrongdoing" by the NoW.

In July 2011, Rupert Murdoch and James Murdoch gave evidence to the House of Commons Culture, Media and Sport Select Committee and denied knowing the full extent of the allegations until evidence in civil cases was requested in late 2010.

James Murdoch told MPs he had not been aware of an email suggesting hacking went beyond a single "rogue" reporter. Two former News of the World executives later issued a statement claiming they had informed him.

James Murdoch was questioned again by the media committee in November 2011 and reiterated his claim that he had been unaware of the scale of phone hacking.