Mervyn bends - and how!
The Bank of England will on Monday morning perform what some will see as one of the greatest u-turns in its 300 year history.
Having been far more conservative than the Federal Reserve and the European Central Bank in the way that it provides financial support to banks, it will announce what may be the world's most ambitious and generous plan to pump money into the banking system.
The Bank of England will offer banks the opportunity to swap their mortgages for rock-solid government securities or, more specifically, nine-month Treasury bills.
It will offer to do so in the form of a standing facility that will remain in place for up to three years. And banks will be able to draw on it on a daily basis, as needed.
The Bank will say that it expects around £50bn of these securities to be issued to banks in the first instance, but that it would be prepared to provide more help if required.
And the scheme will remove any stigma from banks' requests for such financial support, because the fee for the funds will be set at a commercial, risk-based level: there won't be the penal rates or charges that the Bank of England has traditionally demanded for emergency help.
When the dust settles, the proposal will spark controversy - though not because the Bank of England will become directly exposed to the downturn currently afflicting the housing market.
In this kind of long-term collateral swap, the credit-risk on the mortgages being handed over to the Bank of England will remain with the banks and building societies that provided the original mortgages. So if there were a sudden rise in mortgage defaults and the value of the swapped mortgages fell, well then the banks would have to provide new, unimpaired collateral to the Bank of England.
Which is not to say there is no risk for the Bank of England or by extension for the taxpayer. The Bank of England and taxpayers would emerge as losers if there were a collapse of a bank to which it had lent - but, to be clear, a bank collapse would be much more likely in the absence of this kind of liquidity injection.
The real controversy will be over whether the Bank of England is being too forgiving of the sins of our banks.
The Bank of England is, in effect, replacing much of the vital finance banks have raised over the past few years by selling mortgage-backed bonds to international investors.
Since last August, those investors have no longer wanted to buy those mortgage-backed bonds. So British banks have found themselves short of tens of billions of pounds for lending to all of us. Which is one of the reasons why it has become harder and more expensive for many of us to borrow money to buy a home.
But international investors' decision to boycott those mortgage-backed bonds is partly the banks' fault. Arguably many of them lent recklessly and stoked up a housing-market bubble. And it is the pricking of that bubble which has scared off the erstwhile purchasers of mortgage debt.
Now it was only a few weeks ago that Mervyn King was arguing passionately that banks should pay for their mistakes. He now needs to explain why he thinks they have paid enough and have learned their lesson.
Which brings me on to the second reason why the Bank of England should be bracing itself for a storm of protest.
Many bankers are convinced that if this scheme had been in place last August or in early September, Northern Rock would have been able to raise enough money to avoid the humiliating financial crisis that took it from run to nationalisation during an autumn and winter of very public mayhem.
The City watchdog, the Financial Services Authority, desperately wanted such a generous mortgages-for-loans swap scheme to be established months ago. So again Mervyn King needs to say why it was inappropriate in the early weeks of the credit crunch but is highly appropriate now.
Finally there is the fairly important question of whether pumping all this money into the system will do the trick.
Well, the banks are cock-a-hoop, which tells you something. But only the biggest banks will have direct access to the standing facility, so the Financial Services Authority is gearing up to put pressure on those gorillas to pass on some of the new money to the smaller banks and building societies - which are the ones currently experiencing the most acute shortage of liquid funds.
On the other hand, the Bank of England's largesse won't miraculously lead to a great gush of loans to all of us from the credit tap. Mortgages have become less cheap and easy to obtain in part because banks - like many others - fear that house prices rose too high and will now fall for an indeterminate period.
Just because they will have access to new money from the Bank of England doesn't mean they will splash it around in the form of new cheap mortgages, as though the euphoric madness in credit markets of the past few years had never ended.
There's a new climate of caution and prudence in the banking system. That change to grey in the financial weather will endure for months and possibly years.