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The US authorities' decision to let Lehman Brothers fail will be severely criticised by financial historians - the next generation of Bernankes. That precipitated the current acute financial crisis. The Bear Stearns operation had protected counterparties, but after Lehman all remaining trust vanished. Money markets and interbank lending froze completely. Spreads on credit default swaps rose to levels signalling both extreme fear and feverish speculation.

Iceland's Glitnir Bank was among the first casualties. One of the many vicious circles in this crisis ensnared Iceland's banks: they were deemed too risky because the country's central bank seemed not to be a credible lender of last resort, while the government and central bank were deemed not credible because they might have to take over the banks.

The markets hit Glitnir first. Like fellow Icelandic banks Landsbanki and Kaupthing, Glitnir was solvent. All posted good first-half results, all had healthy capital adequacy ratios, and their dependence on market funding was no greater than their peers'. None held any toxic securities. These banks had been managed well since their "mini-crisis" in early 2006.

No matter - when foreign short-run credit lines closed, Glitnir had to request a short-term loan from the Central Bank of Iceland, which refused. Rather than taking Glitnir into administration, the CBI enforced nationalisation on punitive terms. The governor, David Oddsson, was prime minister for 13 years prior to moving to the CBI in 2005. His decision reflected politics, technical incompetence and ignorance of markets, and his comments thereafter were highly destabilising.

This triggered a sovereign debt downgrade and a sharp further fall in the already depreciated krona. Short-run funding for Glitnir and Landsbanki evaporated, margin calls came from the European Central Bank, loan covenants kicked in because of the downgrade. With the banks unable to meet commitments, Iceland's financial regulators put them into administration.

Kaupthing still seemed viable. But last Tuesday, Mr Oddsson made public remarks that were interpreted to mean that Iceland would not meet its obligations to UK depositors. This was politics for home consumption. So was the UK's retaliation, with an ill-considered invocation of anti-terror laws to seize the UK assets not only of Landsbanki, but also of Kaupthing. Gordon Brown's highly aggressive statement was not his best moment of the financial crisis.

Kaupthing was collateral damage. Britain's seizure of its Singer and Friedlander subsidiary destroyed the larger bank, as covenants on loan agreements were activated. The UK and Iceland appear now to have agreed on dealing with depositors, but too late for Kaupthing. Still, it would be foolish for the UK authorities to impair Kaupthing's assets further.

Meanwhile, the krona fell to ridiculous lows offshore, while domestic trading of the currency ceased. The CBI then made two further egregious errors. The central bank had mishandled its interest rate policy and the foreign exchange markets since early 2008. On Monday, it announced a currency peg at a rate well above the market. Without effective controls, this was unsustainable, and was abandoned by Tuesday. The bank also prematurely announced a €4bn ($5bn, £3bn) loan from Russia, but it emerged that negotiations would start only this week. What was meant to restore confidence did the opposite.

The Icelandic banks were highly leveraged and large relative to the domestic economy. So are those of the UK and Switzerland. None has been immune to the devastating effects of the crisis. And there may be significant contagion from Iceland to countries vulnerable to capital flow reversals.

There are further lessons. Politicians should not become central bank governors. Mr Oddsson is part of the problem, not of any solution, and should resign immediately. Allowing partial "euroisation" was a recipe for instability. And Iceland was unable or unwilling to arrange early international support, nor did it wish to call in the International Monetary Fund.

Iceland could now negotiate an IMF programme with conditionality and lending from the Fund. But letting the currency float is likely to be disastrous, even with (or because of) much higher interest rates. They could peg the currency with capital controls. Or they could announce they are entering into negotiations to join the European Union, with a commitment to join the euro. If they do, the eurozone authorities should agree to support a reasonable exchange-rate band.

The debacle is due to the unexpected severity of the financial crisis and shocking policy errors. But Iceland has excellent institutions and human capital, as well as sophisticated service enterprises. Its people will have to absorb a temporary fall in their high living standards. Its banks will be revived as much smaller institutions, still with highly capable managers. It will ultimately prosper again.