Image caption Andy Coulson has been thrust back to the centre of the scandal at the NoW

E-mails have emerged of alleged payments to the police by the News of the World (NoW), triggering fresh calls to investigate the relationship between officers and Rupert Murdoch's newspaper empire.

As each twist and turn of the phone hacking scandal is played out, amid ever more serious claims, pressure mounts on the NoW.

Yet news that the Sunday tabloid's publisher, News International, has uncovered e-mails indicating tens of thousands of pounds were paid over the years to police also places the Met and other forces at the centre of the inquiry.

Celebrities and politicians whose phones may have been hacked have long criticised police for failing to properly investigate, not following up evidence and for being too close to the media.

But the e-mails have led to wider questions about the way the NoW may have obtained its stories and the motivation of the police.

Met Police commissioner Sir Paul Stephenson has confirmed Scotland Yard was handed documents last month indicating "inappropriate" payments were made to officers, and said an investigation had begun.

'Cynical cover-ups'

Paul Farrelly MP, a member of the Commons culture, media and sport select committee which has investigated hacking, has now called for an independent inquiry.

He told BBC Radio 4's Today programme: "Nothing surprises me about the News of the World's behaviour; they've been getting away with cynical cover-ups over a long period of time.

"But what really disturbed us in the committee when we were investigating was the approach and evidence given by the police.

Media playback is unsupported on your device Media caption Brooks: "We have paid police for information in the past"

"They closed the inquiry down; they clearly didn't investigate fully. And it's the question of the motivation behind that, whether it goes beyond normal press relations, that really is the justification for having an independent inquiry."

He said the overall police investigation - Operation Weeting - was not investigating the conduct of the Met Police and its relationship with the NoW, therefore an inquiry was needed, and one where evidence could be given on oath.

The e-mails have also thrust David Cameron's former spokesman Andy Coulson back at the centre of the scandal, as they date from his editorship of the NoW from 2003-7.

It was in 2003, as he sat next to Rebekah Brooks (then Rebekah Wade), as the pair gave evidence to a parliamentary inquiry into the press and privacy, that the question of police payments by journalists first hit the headlines.

Sun editor Ms Wade, formerly editor of the NoW, admitted "We have paid the police for information in the past".

At that point, Mr Coulson quickly interjected, saying they adhered to the editors' code and the law which forbids payment to the police for information.

Mr Coulson stood down as NoW editor in 2007 after royal editor Clive Goodman and private investigator Glenn Mulcaire were jailed for hacking. He said he knew nothing of the offence but took responsibility as he was editor.

He has not commented on the latest allegations, although it has been reported he has told friends he suspects he is being used to deflect attention from News International.

'Abuse of process'

In a letter to Keith Vaz MP in April, Mrs Brooks - now News International's chief executive - said her answer in 2003 had been in response "to a specific line of questioning on how newspapers get information".

Mr Murdoch's key lieutenant denied she had any "knowledge of any specific cases".

The e-mails raise questions about which policemen were paid, which newspaper executives knew money was paid and who handed the payments over.

BBC legal correspondent Clive Coleman said that, if payments were made to officers, it also raised questions about which cases they related to, whether court cases followed and whether people may have the right to appeal based on an "abuse of process".

He said the public would want to know whether any officers named in the e-mails were now under suspicion, and if they were, whether they were involved in the current hacking investigation.

Media commentators have long suspected Fleet Street of practising "dark arts" when it came to gathering information.

But Roy Greenslade, professor of journalism at City University and Guardian commentator, said he never heard of any such payments when he was a senior executive and editor on the Sun and Daily Mirror in the 1980s and 90s.

"Of course, it might have happened without my knowledge. But, on those papers at least, there was no slush fund and any single payment over, say £100, would have raised questions from the managing editor," he said.

"So I very much doubt that any large payments were ever made. I may be guilty of naivety, however."

Roy Ramm, a former head of the Met's Specialist Operations, as well as the Flying Squad, said he was never offered money and had never heard of it happening in his 27 years' service.

"Policemen will always go for a drink and bite to eat with journalists... the relationship can be productive for both sides," he said.

"But I was never offered money. I can't describe that as anything other than corruption."

In September last year, the Met's assistant commissioner John Yates, who has conducted inquiries into hacking, denied any officers had made money out of the NoW.

"There's no evidence of that whatsoever," he told the Today programme.

"Of course, I'm not denying that there's a relationship between the Met Police, other police and the entire police service and the media, but to suggest it's improper you'd have to produce some evidence of that."

News International (NI) has issued its own statement about the alleged payment of police by the News of the World.

It said former director of public prosecutions Lord Macdonald QC had been appointed by News Corp's board to advise NI on the "extensive cooperation" with the Met over police payments at the NoW.

"The appointment, which was made in May, is one of a series of measures to address these issues since January 2011, when information was voluntarily disclosed by News International that reopened the investigation into illegal voicemail interception known as Operation Weeting."

The statement said NI could not comment on the details of the information for fear of prejudicing any ongoing inquiries.

NI was determined to deal "responsibly and correctly" with the issues that had arisen, it added.