Economists who regularly use econometric models are well aware of the problems which arise if those models are not updated frequently. Updating is more than mere mechanical revision in the face of new data. This article will reveal that quite substantial changes have taken place in the National Institute's model as a result of a comprehensive re-estimation exercise, undertaken over the last year, which encompassed most of the behavioural equations in the model. Although there will not be space to describe all of these changes in full, the next section provides a brief account of the main developments. More information on some of the equations is given in an appendix, and the final section of the main text describes the results of a range of simulation exercises using the whole model.