We study how relationships between firms and banks evolved between during the Twentieth century in Britain and we relate it to firms' borrowing policies and leverage ratios. We document and explain a remarkable transition from single to multiple firm-bank relationships during the last twenty years of the sample period. Larger, global, or transparent companies with greater needs for bank credit and specialized services were more likely to add a bank, especially when located in un-concentrating local banking markets. Deregulation and intensifying competition in the banking sector during the 1970s therefore seemingly spurred banks to supply credit and services through multilateral arrangements. Firms that add a bank following deregulation borrow more than similar firms that do not add a bank, and their bank debt expands while their trade (and other) credit contracts. (131 words)