This paper examines the post-compulsory education and training (PCET) systems of England, Wales, Scotland and Northern Ireland, using cohort survey data for the early 1990s. It compares these systems with respect to four issues of current policy concern: participation, inclusiveness, academic drift and parity of esteem. It asks how a system's performance on these four criteria varied according to the degree of 'unification' of PCET, that is, the extent to which academic and vocational tracks were linked or combined within a unified system. In the early 1990s Scotland was the most unified system (with the weakest divisions between tracks) and Northern Ireland the least unified (with the strongest divisions between tracks). The paper finds no clear link between unification and participation in PCET. The two systems with the highest levels of participation were Northern Ireland and Scotland, respectively the least unified and the most unified systems. However the Scottish system was slightly less inclusive than the other three systems, as indicated by a slightly stronger association between participation and prior attainment and/or social class. Academic drift - measured by participation in academic rather than vocational tracks - was more pronounced in Scotland than elsewhere. There was no clear association between unification and parity of esteem, as indicated by the relative educational backgrounds of entrants to vocational and academic tracks: entry to academic rather than vocational courses was more skewed towards high attainers in both Scotland and Northern Ireland than in England and Wales. Participation in the academic track was also relatively skewed towards males in England compared with elsewhere. The paper concludes that there is unlikely to be a simple causal connection between unification and participation, inclusion, academic drift or parity. However it suggests that a strong work-based sector is more important for participation and inclusiveness, while a strong full-time vocational sector is more important for parity and for avoiding academic drift.