Calculating the equity cost of capital using the APT: The impact of the ERM

One of the expected benefits of membership of the Exchange Rate Mechanism (ERM) was a reduction in risk which should lead to a lower cost of capital and foster investment and growth. Using the APT, we investigate the behavior of the equity market risk premium for the London Stock Exchange prior to and during sterling's membership of the ERM. We find that prior to and during the first year of membership the equity market risk premium fell quite dramatically. However, when conflict between domestic and ERM policy requirements arose at the turn of 1991, the equity risk premium increased and continued to do so until sterling's exit, partially wiping out the benefits of membership of the ERM.