The crucial importance of the City of London for the British Empire does not need to be demonstrated . It appears in the commercial relationships between the metropolis and the Empire : an important part of this trade passed through the Port of London and was dealt with by the merchant houses of the City . 1 At the financial level the bill of exchange on London was the medium of financing for international trade , and especially for trade between Britain and its colonies . 2 It was through the City of London that the countless commercial and industrial enterprises abroad were financed ; this raises in its turn the whole problem of the export of British capital in the nineteenth century, at the heart of which the City is once again to be found . 3 This economic importance of the City of London inevitably raises the question of the place of financial interests in British overseas expansion , a major theme of controversy in the debate on British imperialism.4