This article argues that research into preventive and pre-emptive crime control in the United Kingdom has marginalized the historical persistence of the power to arrest and convict on justified suspicion of intent. It traces the genesis of this power in statute law (particularly the Vagrancy Act of 1824) and demonstrates its consistent use in the nineteenth and twentieth centuries. It shows how this pre-emptive power was fiercely defended by police authorities, particularly during the rise of the ‘civil liberties’ agenda during the 1930s, only losing ground when use of these powers became entangled with debates about race relations in the 1970s. Overall, the article argues that ‘pre-emptive’ arrest and conviction on suspicion of intent have been a significant component of UK police powers since the later eighteenth century, and seeks to demonstrate the value of historical criminology in problematizing contemporary debates.