Carney's view is being echoed across the financial sector, and predictions about a coming recession are now widespread, with some banks estimating that Brexit could wipe an average of 4% off the UK's previous growth estimates over the next three to four years.
While he stopped short of repeating recession warnings, he said the United Kingdom faced the prospect of a "material" slowdown in the economy and that risks the Bank had feared ahead of the referendum had begun to emerge.
The move announced in the biannual Financial Stability Report seemed clearly meant to prevent a repeat of the 2007-08 financial crisis, when banks refused to lend to the wider economy in order to keep themselves solvent. When asked what message he had for British households considering a loan, Carney said that central bankers always advise people to be cautious and prepared to weather ups and downs when taking on a major expense.
The chancellor signed a letter with Barclays, HSBC, Santander UK, Virgin Money, Metro Bank, RBS, Nationwide and Lloyds for the banks to make extra capital available in this "challenging time".
There were already signs that the United Kingdom economy was slowing, even before the referendum.
In remarks made at a news conference Tuesday morning, Carney said: "This is a major change". The BOE gained broad new powers over the financial system and an explicit goal of safeguarding financial stability.
Interest rates have been at 0.5% for more than seven years after they were slashed during the UK's downturn and the global financial crisis.
And, yes, he actually used the word "positive" for some of the effects seen post the Big Vote.
In the United Kingdom, the BOE said it has already detected signs in stock markets and commercial real-estate markets that foreign investors are pulling money out of the United Kingdom.
What they didn't seem so anxious about was the resilience of the whole system, which can be a much more toxic issue - as anyone who went through the 2008 crisis will attest.
The BoE said foreign flows of capital into commercial real estate fell 50 percent in the first three months of 2016 and transactions fell further in the second quarter, an extreme example of concern among investors about the referendum. The Financial Policy Committee of the BoE expressed concern over high United Kingdom household indebtedness, especially in real estate.
It is also watching valuations in the commercial real-estate market, the vulnerability of indebted households and landlords, the global economic outlook and fragile liquidity in financial markets.
The Bank will reduce the capital required to be held on banks' balance sheets by £5.7 billion, which it said would help bolster their lending firepower by up to £150 billion. Most economists said Bank Rate would stay at 0.25 percent until the end of next year.
The Bank has stepped up efforts to allay the potential volatility from Brexit by easing capital rules for banks, allowing them to expand lending to households and businesses by up to £150bn.
"The FPC stands ready to take any further actions deemed appropriate to support financial stability", the panel said.