With apologies to Big Ben, the most striking tower on the London skyline is a pickle-shaped building in the financial district known as the Gherkin. Completed 10 years ago near the high point of the international financial market, it is a symbol of London's rise to the top of that market thanks to the Thatcher government's sweeping deregulation of banks during the 1980s known as "The Big Bang."

A major development in The Big Bang was to take away the wall that used to exist between ordinary British banks with government-insured deposits and investment banks that used their capital to take risks. Once British banks began using insured deposits to make risky bets (and in good times lots of money) American banks set up investment banking branches in London to get around the Glass-Steagall Act's ban on combining investment and deposit-taking banks in the United States. By 2000 Glass-Steagall had been repealed.

Then came the collapse of Lehman Brothers in 2008, threatening to take down an entire international banking system. The U.S, British, German, Dutch, French, Spanish, Japanese and other governments poured trillions into bailing out institutions that had become "too big to fail."

That searing experience led to new laws here and abroad designed to prevent banks from making such risky investments that they could again threaten the international banking system and require a massive bailout.

But bank regulation to prevent "too big to fail" is still a work in progress, to put it generously. It's time to pick up the pace.

Last week the Gherkin went into receivership, a reminder that financial markets remain full of risky investments. In the Gherkin's case, the problem was an unwise decision by the investors to borrow Swiss francs that have risen sharply in value in recent years.

But the Gherkin is not the only investment that could go sour. Recently the Bank of America revealed that an accounting error had led it to understate its risks and overstate its capital by $4 billion in a report to the Federal Reserve Board. A study this year by the Federal Reserve Bank of New York found that many banks had poor data on their risks, concluding, "five years after the financial crisis, firms' progress toward consistent, timely, and accurate reporting of top counter-party exposures fails to meet both supervisory expectations and industry self-identified best practices."

Recently the International Monetary Fund warned that a large number of banks remain so large that they are still widely considered "too big to fail." That, it turns out, is a good thing for the banks and a bad thing for taxpayers.

It is good for the banks because the perception that they run no risk of failure means they can borrow funds more cheaply than other banks, allowing them to grow even larger at the expense of competitors. The IMF put this hidden subsidy at about $560 billion for the world's biggest banks.

It is bad for taxpayers because there is still no reliable mechanism for letting a big bank fail without bringing down the financial system. The "Big Bang" blew away the old system of bank supervision.

A new system that adequately protects the stability of the financial system to the benefit of the general public is long overdue.