Language describing urban planning is often reliant on organic imagery, from the 'flow' of traffic, bodily metaphors of cohesion and health, to the 'monstrosity' of unwanted or questionable urban developments. This paper explores metaphors of liquidity, flow and submergence, as used to express ideas of 'good' and 'bad' urban environments in debates around the growth of the large-scale, low-density, explicitly post-industrial planned city of Milton Keynes. Developed in the context of the postwar language of 'overspill', Milton Keynes' reception in print and popular culture suggests tendencies to understand urban landscapes as receptacles for an inert population which would adopt any containing shape imposed by the urban structure. Unlike many earlier planned developments in postwar Britain, Milton Keynes' plan was intended as less an imposition of form on its future inhabitants, than a flexible structure which would facilitate greater agency on individual, community and market-force levels. Through examining the tension between flow and containment, responses to Milton Keynes' early development suggest some preconceptions regarding the role of cities in determining the industrial and social form of its inhabitants' lives, while planned cities proposing to embrace rather than to restrict flow are viewed with suspicion. Over the course of the 1970s, the tone of this language shifted, becoming increasingly fearful of deterministic space and viewing the containment provided by Milton Keynes as a social evil rather than a positive construct protecting the British landscape. Investigating the symbolic language applied to urban planning offers a valuable perspective on the anxieties which can surround planned developments and their perceived sterility, while foregrounding the cultural definitions of landscape which inform the meanings given to new urban environments.