Abstract
This article explores the activities of United Kingdom-based transnational corporations (TNCs) and their affiliates in the United States. It extends UNCTAD's transnationality index to derive a "relative importance index" of the United States-based activities of United Kingdom TNCs. The results indicate that for some highly internationalized United Kingdom TNCs, activities in the United States account for a predominant proportion in their overall activities. In some cases, the United States affiliates contribute over 60% of the TNC's revenues, profits and net assets. The policy implications of such concentration of TNCs activities in a single foreign country are discussed.