A building in Lombard Street, set apart, since 1775, for interchanging bankers' cheques and bills. Each bank sends to it daily all the bills and cheques not drawn on its own firm; these are sorted and distributed to their respective houses, and the balance is settled by transfer tickets. The origin of this establishment was a post at the corner of Birchin Lane and Lombard Street, where banking clerks met and exchanged memoranda.
Railway lines have also their “Clearing Houses” for settling the “tickets” of the different lines. A “clearing banker” is a banker who has the entrée of the clearing house.
“London has become the clearing-house of the whole world, the place where international debts are exchanged against each other. And something like 5,000 million pounds'-worth of checks and bills pass that clearing yearly.” —A C Perry Elements of Political Economy. p. 363.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894