The chairman of new press regulator Ipso will be rated on his ability to determine the public interest.

A minister resigns from the government after a Sunday newspaper exposes his willingness to exchange lewd images with someone he believes to be a young woman. When a second such example of his behaviour is exposed by another Sunday newspaper two weeks later, he announces that he will be leaving parliament at the next election.

And in a third Sunday newspaper, Brooks Newmark MP writes – in a piece that was clearly ghosted for him – ‘I do not blame the media for my downfall. It is for others to judge their behaviour and their ethics.’

Those ‘others’ include Sir Alan Moses, the former lord justice of appeal who now chairs the new press regulator Ipso. And how does Moses find himself sitting in judgement on the media? Our story starts with the recommendations in 2012 of another appeal judge, Sir Brian Leveson.

In his report on the culture, practices and ethics of the press, Leveson called for independent self-regulation. One can argue that this phrase is a contradiction in terms – if the press regulates itself then its regulator is not independent – but the judge’s plan was clear enough: a regulator funded by the press but run by an independently appointed board with a lay majority, and with no serving politicians or editors among its members.

Ipso certainly meets that definition. Its board has 12 members, including the chairman. Seven are independent while the remaining five are mostly former editors who represent the newspaper and magazine industry. It has a separate complaints committee, also chaired by Moses, with a similar split between independent members and media representatives.

But Leveson also made recommendations that Ipso does not meet. Arguably, the most important of these relate to Ipso’s lack of independence: the industry body that funds it retains wide powers over the way it operates. Another concern is that Ipso has not delivered the low-cost arbitration service that Leveson had recommended.

Moses accepts, disarmingly, that Ipso is not ‘Leveson-compliant’. But he insists that it will be independent and he hopes that papers that have not signed up – the Guardian, the Independent and related titles – will join Ipso once they see how it operates.

Leveson recommended the creation of a recognition body to check whether a regulator such as Ipso was independent and effective. The government chose to incorporate the recognition panel by Royal charter, buttressed in the Crime and Courts Act 2013 with potential sanctions for publishers who do not join a recognised regulator. Ipso is not seeking recognition from the chartered panel, chaired by David Wolfe QC.

But another body, the Impress Project, is establishing a regulator that could obtain recognition under the charter as meeting Leveson’s recommendations and trigger the availability of sanctions.

Ipso opened for business on 8 September and the Brooks Newmark case is its first major challenge. Unlike the Press Complaints Commission, which it replaced, Ipso expects individuals to complain initially to the publisher concerned. The new regulator will step in if the publisher fails to resolve matters within 28 days.

But Moses made it clear that the Sunday Mirror, which forced Newmark’s resignation as a minister, should not take that long. Ipso immediately launched its own investigation into whether the newspaper’s use of subterfuge – a male reporter pretending to be a young female party activist – had been designed to generate a story where none existed rather than to confirm existing allegations. The editors’ code of practice (inherited from the Press Complaints Commission) says that subterfuge ‘can generally be justified only in the public interest and then only when the material cannot be obtained by other means’.

The Newmark story had been condemned as a fishing expedition. But Moses regarded that as something of a misnomer. ‘Most fishermen choose to throw their line where they know there will be fish’, he told a meeting organised by the Media Standards Trust. The term was now used for ‘taking a punt with no evidence in advance and, surprise surprise, somebody might be tempted to do something that they regret… that’s hardly a newspaper story’.

I’m not so sure. Is it really in the public interest that someone who promises to seek residential psychiatric treatment after losing a battle with his ‘demons’ should remain a minister, or even stand for election as an MP? Do we want people in government who ‘craved adrenaline and risk’?

On the other hand, a glance at the main party leaders shows how difficult it is to find politicians these days who know about anything other than politics. Perhaps the press should not be deterring candidates with colourful private lives from making a contribution to public life.

So the challenge now facing Moses is to decide what is in the public interest. It is on his ability to judge this elusive concept that he himself will be judged.

Joshua Rozenberg is a freelance legal journalist