Hours after Rupert Murdoch's defiant gamble of launching a Sunday edition of the Sun, the head of the police investigations into illegal behaviour by journalists spelled out startling details of what she called a "culture of illegal payments" at the title.

Deputy Assistant Commissioner Sue Akers told the Leveson inquiry that one public official received more than £80,000 in total from the paper, currently edited by Dominic Mohan. Regular "retainers" were apparently being paid to police and others, with one Sun journalist drawing more than £150,000 over the years to pay off his sources.

"The cases we are investigating are not ones involving the odd drink, or meal, to police officers or other public officials," she said. "Instead, these are cases in which arrests have been made involving the delivery of regular, frequent and sometimes significant sums of money to small numbers of public officials by journalists."

"A network of corrupted officials" was providing the Sun with stories that were mostly "salacious gossip", she said.

"There appears to have been a culture at the Sun of illegal payments, and systems have been created to facilitate such payments whilst hiding the identity of the officials receiving the money."

Akers's reference to the systematic nature of alleged corruption, and its endorsement by senior executives, will be a clear signal to the US department of justice that her allegations, if proved, fall squarely within the ambit of the US Foreign Corrupt Practices Act. Rupert Murdoch's US parent company, News Corporation, could face fines of hundreds of millions of dollars unless it can show it has co-operated vigorously with the authorities in rooting out malpractice.

Akers insisted in her testimony that, although she was dependent on News Corporation's management and standards committee (MSC) to turn over incriminating emails, she was confident the co-operation was working well and the MSC was independent of News International.

She said the investigation into bribery, Operation Elveden, was following Crown Prosecution Service advice to focus on cash payments and not on "more general hospitality, such as meals or drinks". These were specifically excluded from Elveden's terms of reference.

Her testimony contradicts claims by some Sun staff that the paper's journalists – 10 of whom have been arrested over corruption allegations – are being persecuted merely for buying lunch for contacts. After the arrests Mohan published a lengthy anti-police column in the Sun. Written by Murdoch veteran Trevor Kavanagh, it complained of a Soviet-style witch-hunt, and claimed vital press freedoms were under threat by the police raids.

Others claimed the MSC was endangering the sanctity of journalists' sources by turning over information to the police.

Akers told the inquiry that the MSC was handling police requests for information "in a manner that seeks to protect legitimate journalist sources at all times. Our aim is to uncover criminality. It is not to uncover legitimate sources."

The MSC was redacting information about sources before handing it over unless there was an "evidential base" to justify attempts to identify the public official concerned.

She said one police officer from the specialist operations division had been identified "who was seeking payments from journalists with the NoW". He had been arrested last December. But the investigation of two NoW journalists suspected of bribery had so far failed to identify any police they may have paid.

Akers said the move to investigate the Sun as well as the NoW was the MSC's idea. "This review had not been requested by the [Metropolitan police]."

Far from wanting to put the Sun out of business, she said, police had agreed to carry out arrests on a Saturday, when no daily journalists were working.

The emails turned over by the MSC had led to the arrest so far of 10 Sun journalists, two police officers, a member of the Ministry of Defence, an army officer and the relative of a public official "acting as a conduit to hide a cheque payment".

Akers said the 61-strong Elveden investigation was still at a relatively early stage in trying to identify the recipients of illicit cash: "The emails indicate that payments to 'sources' were openly referred to within the Sun … there is a recognition by the journalists that this behaviour is illegal, reference being made to staff 'risking losing their pension or job', to the need for 'care' and to the need for 'cash payments'. There is also an indication of 'tradecraft', ie hiding cash payments to 'sources' by making them to a friend or relative of the source."

Murdoch gave a statement after Akers's evidence saying: "She [Akers] said the evidence suggested such payments were authorised by senior staff at the Sun.

"As I've made very clear, we have vowed to do everything we can to get to the bottom of prior wrongdoings in order to set us on the right path for the future. That process is well under way.

"The practices Sue Akers described at the Leveson inquiry are ones of the past, and no longer exist at the Sun. We have already emerged a stronger company."