Why did the Medici bank go downhill under the management of Lorenzo de' Medici, 1469 to 1492? The present article is about one section only, the London branch, but it may have some usefulness for illuminating the general problem. Since Lorenzo's servants were deeply involved in the trade and politics of London it may also shed some light on English history. The Medici bank was very fully and helpfully investigated by Raymond de Roover. De Roover quoted the general judgements of Machiavelli and Guicciardini that Lorenzo had no commercial luck and stood aside from the business of the bank, leaving it to his representatives. In the case of the English branch he attributed much importance to independent loans to King Edward IV parallel to the Bruges branch's loans to Charles the Bold duke of Burgundy. De Roover made a good deal of progress but his account is not final. There is a vast amount of documentary material relevant to the London branch in the Mediceo avanti il Principato collection in the Archivio di Stato, Florence, and in the exchequer records at the Public Record Office in London. De Roover did not use any of the unpublished London material, and did not refer to many of the relevant records in Florence. This article will not be final either – the Medici bank is an endlessly complicated subject with ramifications in so many areas of European history – but I hope to push a little further into the complex web of evidence and make the conclusions a little stronger.