Immigration control is increasingly being extended from external borders to the interior of the state and society, and irregular residents in particular face policies that directly aim to prevent their settlement, integration and access to services. The British government explicitly presented these as an effort to create a ‘hostile environment’ for this segment of the population. In order to be effective, such policies have to be implemented within the core institutions of the liberal welfare state which, at the same time, fulfil a crucial role for the integration of society as a whole. Based on original interview data from London, this chapter looks at several sites where the exclusionary logic of immigration law intersects with various inclusionary logics underlying public service provision. Organisation theory helps to explain how and why different public institutions (hospitals, universities and local welfare departments) have responded to this by establishing specialised subdivisions that deal specifically with migrant irregularity. This development represents one of many ways in which the politics of (dis)integration can be institutionalised. While it allows welfare institutions to shield their core professional staff from contradictory logics and demands, it further increases the dangerous overlap between their own aim and function and those of the immigration system.