In the United Kingdom (UK), private security contractors are taking on increasingly prominent roles, their market failures are becoming ever more controversial, and the public regulator responsible for controlling their activities – the Security Industry Authority (SIA) – is undergoing major restructuring. Now is therefore a good time to reflect on the successes, failures and prospects of UK security regulation. With this in mind, the article advances an up-to-date and comprehensive evaluation of the SIA's regulatory practices. Its headline findings are twofold. First, the picture is mixed: the SIA has succeeded in meeting its two core regulatory objectives – to reduce criminality and to raise standards – but only to a degree. Second, context matters: in order to understand SIA's performance, it is necessary to interpret its activities within the broader UK regulatory environment, in particular, the Better Regulation agenda.