In addition, it also had to weigh carefully the advantages of providing lender-of-last-resort assistance to the banking system to avoid a drop in its revenue stream against the risk of lending to an insolvent institution and making a loss that could decrease its capital base and threaten its reputation as the supplier of the ultimate settlement asset. Similarly, central banks had a natural interest in ensuring the ability of the banking sector as a whole to meet the public’s demand for liquidity. The reason for this is that if it allowed a  1  For further details see Stephen Millard and Victoria Saporta (2005): Central banks and payment systems: Past, present, and future. See also Ben Norman, Rachel Shaw and George Speight (2006): The history of interbank settlement arrangements: exploring central banks’ role in payment systems. BIS Review 130/2007  1  solvent commercial bank to fail as a result of a bank run, it would only aggravate the situation and this could ultimately result in a more general run on the banking system and ultimately on itself. As a result, financial stability became a concern for central banks. Moreover, for the central bank as the provider of the ultimate settlement asset, it was also important to maintain monetary stability. In particular, if the central bank printed more and more of its banknotes without a corresponding increase in the demand for them, the notes would fall in value relative to those of other banks.
The recent developments were triggered by a perception of higher credit risk originating from a perceived deterioration of the credit quality of assets held both by banks and by special  BIS Review 130/2007  3  investment vehicles, with which banks were associated either through liquidity commitments or reputation issues. The situation deteriorated when liquidity buffers of banks were put under stress by the need to meet their liquidity commitments and to take on their balance sheet assets which had become illiquid. Then, banks also became unwilling to provide unsecured lending to other banks, in particular at longer maturities, because of uncertainty whether they would themselves obtain liquidity if needed. Once this stage was reached, the deterioration of liquidity conditions became self-reinforcing, and turned out to be painfully durable, as can be seen for instance from the still exceptional three-month EURIBOR spread relative to three-month repo rates. What could central banks do about this? First, they provided extra liquidity through open market operations. This not only contributed to bringing down short-term interbank rates to target levels again, fulfilling monetary policy implementation purposes, but may also have contributed to supporting the willingness of banks to lend. Second, accepting that availability of central bank eligible collateral is the ultimate line of defence against illiquidity for banks, many central banks widened the set of eligible collateral. For instance, the central banks of Canada and Australia took such actions, and also the US Fed clarified that it would accept certain instruments in its discount window.