If international finance was a country, it would be run as a one-party state.

Few deviate from the party line. If they do, they don't last long.

For the last seven years the rest of the world has been forced to notice. Those who move money around might as well have their own flag, envoys and laws. Invariably they behave as though that's the case.

Claiming their own form of diplomatic immunity on behalf of Bankistan is a particular speciality of its citizens. Did one of their number breach our local customs, or even - very regrettable - a law or two? Just a bad apple.

Is their distressing evidence of, say, wholesale fraud perpetrated on millions in dozens of otherwise welcoming countries? According to the Bankistan party line, mistakes - always "mistakes" - were made in the past by people who are no longer around to answer for their actions. These errors will never be repeated. You have their word.

But why, naïve souls might ask, do things go so catastrophically wrong so often? The party line, heard everywhere since the latest scandal at HSBC, is very firm. Those who are not Bankistan natives simply don't understand. Not only are things too complicated to explain, they are too complicated for any one individual to master.

We heard this a lot when the banks came close to collapse. Vast private markets in exotic financial instruments had gone awry, among other things. When the outcry had subsidised a little, an astounding explanation was ventured. No one quite understood the instruments that were supposed to protect against all risk. Besides, big modern banks were just too "complex" to allow those in charge to be, well, in charge.

The complexity defence has been offered repeatedly in the case of HSBC and Lord Green, erstwhile chief executive and chairman, latterly a government trade minister. Just as he was oblivious to his bank's lurid career as a money launderer to the Sinaloa Cartel, so he knew nothing of goings on at HSBC's Swiss private banking arm when it was tutoring assorted dictators, crooks and other ne'er do wells in the art of tax evasion.

It might be true. Running an organisation with a quarter of a million employees around the world and around $2.7 trillion in assets cannot be easy. By most reckonings, HSBC is the world's second-biggest bank and one of Britain's biggest companies. But do those facts excuse an extraordinary ignorance of the outright crookedness permeating one of the bank's four main business groups?

A lot has been made of Lord Green's status as a lay Anglican preacher and moral arbiter in the world of banking. He has written extensively on the need for ethics when dealing with Mammon. In 2009, in fact, he said in an interview that "our word is our bond and the idea that you can play fast and loose with that is immoral". Less has been said recently about his failure to mention the impossibility - as his defenders argue - of keeping his big, complex bank on the right side of the law.

If the job is beyond a single person, or even a team of executives, why was Lord Green in his post, accepting a "base" salary (multiplied many times over) of £1.25 million? Why, for that matter, was he ushered into government and the Lords in 2010 when leaked information on crookedness in Switzerland had already reached HMRC?

No personal wrongdoing is suggested, of course. Then again, where Bankistan is concerned, only hapless lowly "rogues" ever face the consequences of their actions. When they pause in their fury, this is the aspect to banking's serial crimes that ordinary people, knowing that minor benefit frauds can earn jail time, fail to understand or accept. Of 1,100 names handed to HMRC, only one has attracted a prosecution. That individual, it turns out, was already under investigation.

Once again, complexity is adduced. Meeting standards of proof, wringing co-operation from the Swiss: it's all very tricky. As with the failure to prosecute anyone of consequence in the aftermath of the banking crisis, the latest HSBC scandal has bested - so it is claimed - Her Majesty's Government. We are supposed to console ourselves with the fact £135m in tax, interest and penalties has been recovered.

Divide that figure by 1,100 and the average return - just under £123,000 - isn't so impressive. This is especially true since HMRC seems to have favoured a style of "negotiation" generally unavailable to ordinary mortals. It is wholly underwhelming if you know the tax authorities were first handed 7,000 UK client names in 2010, and that those clients held $21.7bn with HSBC.

Who needs a private Swiss bank account and why? The bank has said there are "numerous" good reasons, but has neglected to name one. You might want to do business in Switzerland, of course, or perhaps buy property there. The revelations from Panorama, the Guardian and others - neither rebutted nor refuted by HSBC - say we can forget such benign explanations. One of Britain's biggest companies was up to its neck, under the leadership of its preaching chairman, in crookedness.

Simple enough questions: why was any of this allowed, and why was the bank not pursued when the evidence emerged? We have been told that HSBC was just to big to be run properly. We have heard often that Britain's banks are too big to fail. It should be obvious enough by now that Bankistan and its City enclave are also too big for British politicians - had they the will - to control. The treatment of banks is preferential because they insist on no less.

Watching Tories and Labour attempt to exchange blame for HSBC would be funny if this was fiction. Did Ed Miliband's party fail to regulate banks adequately and fail to do much about tax evasion and avoidance? There's not much doubt about that. Did David Cameron and his team call for still more "light touch" regulation before the crash and then drape the then Stephen Green in ermine? Unquestionably.

Both parties put themselves forward as the only rational candidates to lead the next government. You can count it a comforting thought, if that's your taste. Like the banks, both assure us the "mistakes" of the past will never be repeated; that individuals long departed were to blame; and that dealing with Bankistan is, after all, a complex business. The envoys of international finance have taught them well.

If the rest of us have learned anything, it ought to be this: what began to unfold in 2007-2008 was our glimpse of reality and it must not be forgotten whenever amnesia is urged upon us. The crisis and what it revealed were not just capitalism's little blips. They were not just the price we pay for a system that suffers a little wobble every few decades. That system is a form of organised corruption.

Lord Green has thus far refused to make any comment on what took place in Switzerland while he was earning vast sums and claiming to run HSBC. Perhaps he is preparing a sermon instead. Matthew 21:12 rarely fails.