This article explores vertical and horizontal dimensions of the work of public, private and civic leaders involved in economic development in England, in particular, those working in the complex terrain of Local Enterprise Partnerships, a key partnership tool in the UK central government’s localism agenda for driving growth. It offers insights into innovative ways in which state, non-state and citizen agents navigate a complex set of vertical, legal authority structures within fragmented, horizontal and largely informal new ‘spaces’ of interactions/interrelationships to collaboratively co-produce strategies and plans for transforming local areas. To advance our knowledge of collaborative leadership requires new methodological approaches to investigating multi-accountabilities and how co-production works within ‘loosely coupled’ networks. It is imperative to appreciate the problems associated with leadership working across sectoral boundaries within complex networks of vertical, legal structures and horizontal, informal action spaces. In such networks, leaders, as institutional representatives, work collaboratively to achieve objectives not readily attainable by member organisations acting alone. They also need to compromise and negotiate their representative role back to a parent organisation while protecting and promoting the priorities, aims and interests of the new entity, in this case, a Local Enterprise Partnership. Theoretically, then, the article is located in recent debates on the theory and practice of New Public Governance, to show the inadequacies of New Public Management models for capturing the complexities between formal authority structures and fragmented informal sets of relationships. It also draws on accountability models, notably, from the Utrecht School, to identify social relations between collaborative leaders on Local Enterprise Partnerships, and to show how they assert agency and individual actions within the boundaries of participating institutions.