Media playback is unsupported on your device Media caption Sun editor Dominic Mohan: "Phone hacking was well known"

The editor of the Sun has told the inquiry into press ethics the paper can be a "powerful force for good".

Dominic Mohan said this came about through its campaigns, support for charities and its efforts to explain complicated stories in a clear way.

Mr Mohan also told the Leveson Inquiry over-regulation could deal a "mortal blow to the newspaper industry".

Earlier, former Sun editor Kelvin MacKenzie defended his "bullish" approach to journalism.

But Mr MacKenzie, who edited the paper from 1981 to 1994, said subsequent editors had become more cautious "in a changing world".

Mr Mohan and Mr Mackenzie gave evidence at the Royal Courts of Justice on the first day of the inquiry since its Christmas break.

The Sun's showbiz, royal and picture editors also gave evidence, along with Justin Walford, News Group Newspapers' editorial legal counsel.

Mr Mohan cited the Sun's support for the Help for Heroes campaign, as well as its ability to offer a "quick, digestible summary of very complex issues", as evidence that the tabloid, which sells 2.6m copies per day, could be "a powerful force for good".

Meanwhile, Tuesday's edition of the Times newspaper is reporting that Prime Minister David Cameron is expected to be asked to appear at the inquiry in future to answer questions about his relationship with the Sun's owner Rupert Murdoch.

A Downing Street spokesman said a request has not yet been received but Mr Cameron would attend if asked.

The newspaper also said former PM Gordon Brown and Labour leader Ed Miliband would be asked to give evidence.

Private investigators

Analysis They were two contrasting accounts. One detailed how the Sun now conducts its business. The other was an account of how Britain's most popular newspaper once operated. Dominic Mohan, the current editor, insisted ethics played a strong role; he'd fostered a culture of honesty and integrity; and although he sometimes talked to Rupert Murdoch several times a week, the owner had never tried to interfere with the tabloid's editorial stance. By contrast, Kelvin MacKenzie, who was in charge for 13 years, talked about his "bullish" approach and about his view at the time which was that "most things should be published". Mr MacKenzie's testimony was colourful and provoked laughter when he mimicked the former prime minister, Sir John Major. But it is evidence which won't have helped his former employer, News International. Inquiry tweets from Peter Hunt

In his evidence, Mr Mohan admitted private investigators had been used in the past "without the permission of the chief executive officer" but there were now new controls in place.

When asked if he, during his career at the tabloid, had ever used private investigators, Mr Mohan responded: "Not to my knowledge, no."

Mr Mohan said he had used "search agents" to obtain ex-directory numbers, but he said he would not describe them as private investigators. In his written evidence he states that search agents charge between £50 and £300 a time and the Sun has spent about £165,000 on them.

Mr Mohan said he had a close involvement on issues involving the Press Complaints Commission and potential legal points.

He added: "At the moment it feels almost every story has to be considered in terms of the Bribery Act, privacy, the PCC."

"I've seen mistakes made over the years and I've learnt from those mistakes," he said, citing a PCC adjudication against the paper for printing a story about Charlotte Church's pregnancy. He said as a result of the adjudication the paper had not run stories about women who were under 12 weeks pregnant.

He told the inquiry the newspaper was considering appointing an independent ombudsman to deal with complaints from readers.

Mr MacKenzie said earlier that he did not replace the Sun readers' ombudsman - who had died - because there were so few complaints.

Mr Mohan was asked about reports that in 2002 he thanked "Vodafone's lack of security" for exclusive stories in rival paper the Daily Mirror.

It's so hard in life, in the press, in the law, to get things 100% correct Kelvin MacKenzie, Former Sun editor Ex-editor defends Sun journalism

"I can't remember my exact words but I believe I said something along those lines… It was said purely as a joke," he said.

"It was a cheap shot at the Mirror, attempting to undermine their journalism because they had a particularly good year."

He said it was not based on any evidence and "was just the Fleet Street rumour mill".

He said he feared that over-regulation could kill the newspaper industry.

He said his "heart sank" when he wrote the Sun's front page on an injunction obtained by footballer Ryan Giggs because he realised there were "several million people out there who already knew that".

"One thing I would ask is that there's a level playing field [between the internet and the press]… because I do think it could be a potentially mortal blow to the newspaper industry that's already wounded.

"I think the combination of an over-regulated press with an unregulated internet is a very, very worrying thought for an industry that employs many thousands of people."

'Lob it in'

Earlier, Mr MacKenzie stood by comments he made in a Leveson Inquiry seminar in October, when he said: "My view was that if it sounded right it was probably right and therefore we should lob it in."

However, he defined "lob" as "to throw in a slow arc", adding: "The point I'm making is that we thought about something, and then put it in."

Mr MacKenzie suggested there was "no absolute truth in any newspaper" and said it was "hard in life, in the press, in the law, to get things 100% correct".

Asked by counsel to the inquiry Robert Jay QC whether he had any regard for privacy while editor, Mr MacKenzie said: "Not really, no."

He said his view had generally been that "most things, as far as I could see, should be published".

But Mr MacKenzie said that attitude had changed at the Sun after his departure.

BBC political correspondent Ross Hawkins, at the inquiry, said the tone of Mr MacKenzie's evidence contrasted with the very sober, downbeat account from Mr Mohan.

Balancing act

Earlier, Gordon Smart, the editor of the Sun's "Bizarre" showbusiness column, said he had no knowledge of phone hacking at the newspaper.

Mr Smart said that the advent of social media had put reporters under more deadline pressure.

He said his job was a balancing act between public interest and individual right to privacy, and said "we act responsibly at all times".

Royal editor Duncan Larcombe also told the inquiry that he had seen no evidence of phone hacking at the Sun. He said that there was an "obsession with getting stories right" at the newspaper.

And the Sun's picture editor John Edwards discussed, among other things, photographs of Hugh Grant with his baby daughter, and a heavily-pregnant Lily Allen. He said balancing public interest and intrusion into privacy was "a difficult line to walk".

Later, Mr Walford said he would be shocked if phone hacking had taken place at the Sun.

"I can say on oath to you that I have never seen anything at the Sun to suggest it was happening," he said.

Mr Walford provoked laughter when he said he had "libel read" news stories produced under Mr MacKenzie's editorship, and "saw the lobbing in" of articles at the time. But he added: "Things have changed very radically from that period of time."

Mr Mohan was the first of seven current national newspaper editors who will give evidence this week.

Statements from former editors of the Sun, Stuart Higgins and David Yelland, as well as Simon Toms, a lawyer advising News Corporation, were admitted as evidence.

Opening Monday's hearing, Lord Justice Leveson said that his inquiry would continue regardless of the outcome of the investigation into how messages on murdered schoolgirl Milly Dowler's phone were deleted.

Allegations that the News of the World deleted messages from Milly's phone when she was missing prompted Prime Minister David Cameron to launch the inquiry.

However, in December, Scotland Yard said it was "unlikely" that News of the World journalists had deleted the messages.