This thesis examines the growth and significance of private security in the United Kingdom. It details the broad commercial functions and lack of public accountability of the private security sector and draws out the implications for civil liberties and public policy. This is a subject which has been seriously neglected in criminology, sociology and related disciplines in Britain. This thesis is the first (publicly available) criminological study of private security in Britain to bring together such a range of material and concerns. It draws upon original 'case-study' observational field-work and on interviews with a wide range of respondents, in private security, the police, Parliament, journalism, trade unions, civil liberties groups and academia. Extensive literature review and collaborative work with various involved parties also support the research. An introductory chapter provides background to the research and outlines the structure of the thesis. The second chapter presents two 'case studies' based upon the observational field-work, discusses aspects of methodology and draws out those points which broadened the nature of the research project and those which have particular relevance for subsequent chapters. The next chapter discusses the range and activities of the private security sector. The chapter on the issue of licensing examines 'causes for concern', present arrangements for self-regulation, the role of the professional associations and of the Home Office, considers the experience of other jurisdictions and generally presents the case for public regulation and accountability. A theoretical chapter charts the conditions conducive to the post-war growth of private security, takes issue with previous theoretical accounts and develops an analysis in which political relations with and within the state are forefronted. A concluding chapter offers cautionary comments on the limits and desirability of some possible future developments and adds thoughts on one possible avenue for policy development.