Metro Bank has the problem so pointedly observed by the great Walter Bagehot in 1873: “Every banker knows that if he has to prove he is worthy of credit . . . in fact his credit is gone.”

Your editorial “Metro panic shows need for proactive regulation” (May 14) says “Metro’s loan book . . . is fully covered by customer deposits.” Of course, customer deposits are not inherently stable — they are inherently unstable. Their stability, as you suggest, is solely due to the guarantee provided by the government.

This fact, so humbling for bankers, has powerful effects, most strikingly shown by the collapse of the US savings and loan industry in the 1980s. Savings institutions that were irredeemably insolvent were nonetheless able to keep their deposits because they were guaranteed by a government deposit insurance fund. However, this fund, the Federal Savings and Loan Insurance Corporation, was publicly admitted to be itself broke! But the depositors correctly believed that behind it all the time was the US Treasury, as in fact it was. This allowed many insolvent S&Ls to keep funding disastrous speculations, which made the ultimate cost to the Treasury far bigger.