In recent years, mortgage markets in the UK have undergone substantial structural change. One important result has been that households are, generally, no longer facing situations of mortgage rationing, whereas for most of the post war period, mortgage queues were commonplace. Although regime switching between rationed and unrationed periods has important implications for the housing market and for the economy generally, the techniques currently available for analysing these implications are limited. The thesis has three aims: (i) it proposes a new, relatively simple way of estimating directly separate mortgage demand and supply functions and hence the extent of mortgage rationing. The approach is capable of taking into account regime shifts and yet does not require disequilibrium estimation techniques. The proposed measure covers the period 1963-1984, conforms closely to a priori expectations and shows clearly the regime shift in the early eighties. (ii) an econometric model of building society behaviour and the housing market is constructed, which demonstrates the importance of the new measure of rationing. (iii) the thesis then examines the impact of the ending of rationing on both building societies and on the personal sector. In the latter case, the effect on housing and asset accumulation decisions is taken into account. The model is also used to examine quantitatively the importance of policy changes under conditions of rationed mortgage supplies relative to the situation in which mortgage supplies are unrationed.