The Census provides spatially detailed information on internal migration within the UK. It is only available decenially, however, so during inter-censal years it is necessary to rely on the NHSCR as an alternative measure of population movement. The value of the NHSCR in the analysis of migration and its suitability as an input to the procedure for projecting sub-national populations remains uncertain. This thesis examines the relationship between NHSCR and Census-derived migration data for a common period (1980/81) and illustrates the conceptual and measurement differences and similarities between the two. Although a strong correlation between the respective patterns of migration is evidenced, significant spatial and age-sex discrepancies in the measured levels of population movement are observed. The presence of Armed Forces and student moves and the phenomenon of multiple/return migration, particularly amongst young adults, are cited as major reasons for the differences. Given an understanding of the characteristics of each type of data, the thesis undertakes to illustrate spatio-temporal patterns and trends in migration since 1970 using both transition and movement information. A reduction in the level of migration throughout the seventies and early eighties has been followed by an increase in the general propensity to migrate, with increasing decentralisation processes moving people away from the most densely populated areas, but with an increasing attractiveness of the South East, particularly Greater London, to young, mobile adults and a net loss of migrants from North to South. The illustration of contemporary trends in migration using time-series data highlights the potential shortcomings of a sub-national population projection model based primarily on 1981 Census information. The thesis critically examines a number of features of the migration component of the OPCS/DOE projection procedure using NHSCR migration data, and suggests possible improvements to the methodology.