This paper examines the impact of regulatory announcements which affect competition, pricing policy and the supply of services in the telecommunications industry on British Telecom's (BT) systematic risk, as measured by the beta coefficient of a market model. Changes in investors' perception of a company's systematic risk will of course also change its cost of equity capital. Since BT's beta coefficient is found to be unstable over the estimation period, the market model is estimated using a time-varying parameter model. The results suggest that announcements which allow the price of BT's services to increase and announcements affecting its supply of services are likely to have an impact on BT's cost of equity capital, since they affect the investor's perception of BT's systematic risk. However, our analysis does not detect any effect from the other types of announcements tested. Further examination of the individual announcements included in the groups reveals that, within the non-significant groups, many individual announcements are significant, but they affect beta in opposite directions and thus no prediction can be made on the sign of their aggregated impact. These findings suggest that when one company dominates the industry, such as in the case of the UK telecommunications industry, the actions of the regulator do not always have the expected effect and problems of regulatory capture are likely to be present.