Drawing on data from a three-year study (2008-2011) of partnerships of schools and colleges delivering the 14-19 Diplomas in England, this article examines how the dynamics of local partnerships were shaped by a contradictory policy landscape in which some policies strongly promoted collaborative working whilst others reinforced competition between institutions. Semi-structured interviews with 136 Diploma consortium leads and case studies of 30 Diploma consortia were undertaken. Most partnerships founded in direct response to government demands for collaboration were strategically and operationally less effective than those that had been formed earlier as a positive, dynamic response to locally identified interests/needs and had evolved over time. When key levers towards collaboration were removed by the new UK Coalition government (2010) and new policies restated the arguments for institutional autonomy and competition between institutions, the fragility of the "enacted" partnerships became immediately apparent. Although members of Diploma consortia with a history of effective partnership working remained committed to the principle of collaboration, other policy developments such as the introduction of the English Baccalaureate and the recommendations of the Wolf Review on vocational education contributed to uncertainty about whether partnership working could, or indeed should, be sustained. (Contains 2 tables and 1 figure.)