A week that began with dramatic headlines about international money laundering, sanctions busting and celebrity tax avoidance on a global scale ended with near meltdown in Downing Street as a political and media storm engulfed the hapless David Cameron. The revelations contained in the leaked Panama Papers have serious implications for leaders, governments and businesses around the world. But for Cameron, they have boiled down to damaging questions about trust, leadership and personal competence. Addressing the Conservative party spring forum, the prime minister apologised for making a mess of things and promised to publish his tax returns over the past several years. “I could have handled this better,” he said.

So proficient at PR in his early days, Cameron’s skills deserted him last week. Perhaps the vitriol heaped on him and his faltering EU referendum campaign are proving too much. Perhaps he genuinely felt his late father’s business affairs, and those of his immediate family, were off limits. He was, he said, “very angry about what people were saying about my dad”. Perhaps that Easter holiday break in Lanzarote was not long enough. Whatever the reason, Cameron and his advisers bungled in not grasping earlier in the week that full disclosure of his past offshore investment activities was essential and unavoidable. It is not convincing to keep on repeating that he and his wife did nothing illegal, cashed out years ago and paid their tax bill in full. By holding money offshore, they presumably benefited from a lower-taxed return than was available at home – or else why bother?

In terms of his past use of offshore tax refuges, the consequent potential reduction or avoidance of domestic tax liabilities, Cameron failed to meet the higher standards he and his chancellor, George Osborne, have repeatedly urged on others. This is not a crime. It is not a resignation matter. It is not a reason to jail Cameron. The issue must be kept in reasonable perspective. But it is disappointing. It is a taint. Even in a cynical age, the past few days’ perception of ducking and diving is not what voters want in a British prime minister. And it is almost certainly not over: there will inevitably be demands for publication of his tax returns in the years before he became PM, including when he was at Carlton Television. Parliament may insist on a formal statement and more grilling next week.

Cameron’s plight serves to illustrate the bigger issue of the deficit in transparency, accountability and trust

The contents of the Panama Papers, taken as a whole, are both sensational and banal. It is amazing to discover, for example, how the Syrian regime of Bashar al-Assad squirrelled away vast amounts of ill-gotten cash with the help of Mossack Fonseca, the now notorious Panamanian law firm; easy-come, easy-go tax haven rules in the British Virgin Islands; and a blind eye from HSBC’s compliance department in Geneva. But while the details are enthralling, the idea that Assad and his cronies are venal and corrupt thieves is hardly earth-shattering. Some of this outlaw president’s honchos have been under US sanctions since 2007. Their bottomless greed was one of the factors that fuelled the Syrian uprising in 2011.

We found out, too, that Vladimir Putin, Russia’s ruthless leader, stands at the centre of a billion-dollar money-laundering network. Moscow’s post-Soviet kleptocracy has flourished in the Putin era – and been closely examined in recent years. If Putin is willing fundamentally to flout international law by annexing part of a foreign country, why would he and his pals hesitate to subvert lax financial regulations? Putin says the whole Mossack Fonseca scandal is a western conspiracy – and the Russian public apparently believes him. It is enough to make a cynic of a saint.

Yet clearly it is not enough to intone regretfully that it has always been thus and always will be, to declare that whatever the Bible says, the rich get richer and the meek inherit the mess. Dictators, war criminals and serial human rights abusers aside, there is a host of influential political leaders and administrators, large banks and businesses, and individual celebrities and sportspeople whose names appear in the Papers and from whom better might have been expected. Thus Cameron’s sorry plight serves to illustrate in a powerfully salutary manner the much bigger issue of the continuing deficit in public affairs of transparency, accountability and trust.

If Cameron is to redeem himself, then progress in this crucial area must be his new focus, starting with next month’s London conference on fighting corruption. But since the 2008 financial crash, it has been clear that, in this field at least, the developed world leads the way. It was the lamentable misjudgments and reckless overreaching of some of the biggest British, American and European banks and financial institutions, not wretched political crooks in Lahore, Doha or Buenos Aires, that plunged much of the world into avoidable austerity and recession. It was the rigging by dealers and traders of undersupervised markets that depleted the pension funds of so many working people. Now, as the Papers reveal, it is western governments that continue to tolerate and facilitate the speculative, opportunistic and often illegal exploitation of a largely privately owned, opaquely operated global financial system that woefully lacks strong, independent controls, an agreed rule book and effective supranational regulation.

It is no use asking China to take the lead. President Xi Jinping’s depressing response to the Mossack Fonseca leaks was to censor the news. It is no use asking the irresponsible, paranoid Putin. And it is no use asking other leading developing countries. South Africa is mired in corruption of its own making. Brazil is struggling with the mother of all political scandals. The impetus for global reform must come from the west. But no single national authority has sufficient clout. While the US tries to project its jurisdiction overseas, such arbitrary unilateralism should be resisted.

What is needed now is an authoritative new body, overseen by the UN. In the past, the UN has repeatedly taken an oversight role in security, peacemaking, and arms control. Now, in these times of recurrent economic turbulence, market manipulation and fiscal skulduggery, a powerful new international financial regulatory body is urgently required. Its remit: to set rules, enforce standards, scrutinise questionable transactions and expose and punish the pinstriped miscreants and their greedy clients whose casual immorality threatens the wellbeing of all. Its mission: to restore trust.