THAT a Conservative prime minister who comes from a wealthy family, should have benefitted from a “tax-efficient” offshore trust should come as no surprise. Bears defecating in woods come to mind. What did surprise was the difficulty David Cameron got into trying to explain it. It was an object lesson in media mismanagement that will be cited by spin-doctors and press advisers for years to come.

Number Ten made four successive statements insisting that Cameron did not benefit from an offshore trust, before finally admitting that, yes, he had benefitted from such investments which he sold when he became prime minister. It's not big money. Many tax haven plutocrats probably spend more on an annual service for their yachts than the £30,000 that the Camerons had invested.

Cameron has also benefitted from the legacy left by his father derived from the Blairmore investment trust that he ran for 30 years. But Ian Donald Cameron did nothing illegal in using that trust to avoid paying UK taxes. And nor did his son. It is a sign of the changed times, post Panama Papers, that these relatively trivial financial arrangement should have caused a political crisis.

I'm not trying to defend the Prime Minister here. He did attack tax avoidance by people like the comedian Jimmy Carr, and he did lobby Brussels to try to protect the secrecy of offshore trusts. So he has arguably been exposed as a hypocrite. He is also collectively responsible for the whole sordid system of industrial-scale tax avoidance perpetuated by successive governments.

But then you could argue that the entire British public are in the dock for aggressive tax avoidance since Royal Bank of Scotland, which is still largely state-owned, has been revealed as one of the most assiduous patrons of Mossack Fonseca, the Panamanian legal firm that set up shell companies to help wealthy people hide their wealth. RBS has been heavily involved in questionable banking using Britain's network of tax havens, including Cayman, Jersey and the British Virgin Islands where it can conduct its business free of tax and regulatory burdens.

We all knew tax avoidance was a big business, but it is very rare that our worst suspicions are so comprehensively confirmed. Most of the dodgy schemes were so opaque and difficult to understand, that the general public remained largely unmoved. Not any more. It is the sheer scale of the Mossack Fonseca leak that has elevated tax avoidance from the business pages and specialist publications to a global political crisis.

Thanks to the International Consortium of Investigative Journalists who broke down the 11 million documents into bite-sized chunks and put names and faces to the schemes, this scandal has profound ramifications. Last week it exploded onto the desks of political leaders from Iceland to Argentina, from Russia to Britain. It is the company the PM now keeps that makes this so damaging: Mubarak, Gaddafi, Putin, Cameron. It doesn't look good.

There have been calls for Cameron to resign, like the Icelandic prime minister, Sigmundur Gunnlaugsson. Though the latter was a much more serious case in which Gunnlaugsson's wife was holding undeclared investments in Icelandic banks while the prime minister was supposed to be regulating them. Unless more emerges about the UK prime minister's offshore financial affairs, it seems most unlikely he will step down.

But the damage has already been done. The headlines have been appalling – especially in nominally pro-Conservative papers like the Daily Mail and the Daily Telegraph. There have been allegations that the pro-Brexit proprietors have been exploiting this opportunity to take a pot shot at the PM for leading the campaign to keep Britain in the European Union.

Cameron has also been attacked for using public money to produce a pro-EU leaflet to be distributed to all households. Even this has been off-shored since it emerged they were printed in Germany. How bizarre if Britain were to vote to leave Europe because voters were so disgusted with the tax affairs of the prime minister. Stranger things have happened.

Cameron has demonstrated that merely being involved in an offshore financial arrangement is now enough to besmirch the integrity of the investor. The shutters are going up in every dodgy bank from here to the Turks and Caicos Islands as law firms that were in the same business as Mossack Fonseca try to conceal what they have been doing. Manufacturers of paper shredders must be making a fortune.

But there is surely no hiding place. Assuming the HMRC, the Serious Crime Office and other agencies like the Bank of England's Prudential Regulation Authority get off their backsides, they could be investigating dodgy arrangements, often involving senior politicians, all the way till the next general election. They will need a lot of extra staff just to track down the thousands of British citizens who have been involved in his scandal alone.

Of course, you could well say that it is a dismal reflection of the state of business regulation and the diligence of our tax inspectorate, that it took a hacker to reveal the extent of what has been going on. Surely the Revenue knew about all this. Why did they do nothing before now? Was it because they thought, like the politicians, that it wasn't in the national interest to expose the tax haven world to public scrutiny?

Labour is arguably as culpable as the Tories in this regard; perhaps more so. You would have expected a nominally left-wing government to do something about the misbehaviour of the wealthy. Where was Gordon Brown when all this was going on? He must have known about the activities of the banks and their use of Britain's “treasure islands”.

Brown is probably the world's greatest expert on stealth taxes and engaged in the most obscure tax manipulation to achieve his budgetary ends – such as the abolition of advance corporation tax credits on pension funds. This was so complex, only three people in the country, Brown, Blair and the governor of the bank of England, understood it until it drained £5bn a year from British pensions.

Like all chancellors, Gordon Brown would certainly have been fully briefed by his civil servants about how our financial services industry uses the network of 17 crown dependencies and territories across the world to pursue business. He entered into a devil's bargain with the City of London to give them what he called “light-touch regulation” in exchange for the turning the City of London into a global banking hub.

But though his predecessors share blame, it happened to be on David Cameron's watch that this scandal emerged. He has an opportunity to rehabilitate himself. Next month he will be presiding over a global anti-corruption summit in London. Many believed that this would be just another talking shop, an opportunity for meaningless hand-wringing by the privileged.

But perhaps Cameron will surprise us, calling time on the British tax havens like Cayman and the British Virgin Islands by announcing that there is to be a proper register of beneficial ownership of businesses and trusts. Full and frank disclosure. It won't stop rich people looking for ways to avoid tax, but it would put an end to one of the most egregious forms of semi-legal corruption conducted in the Queen's name on Britain's “paradise islands”.