In this paper we discuss new evidence on the performance of British Telecom before and after privatisation. We use a unique data set based on company accounts over forty years (1960-1999), and original data kindly provided by BT. For some output data we go back to 1915. We focus particularly on output, prices, revenues, costs, employment, productivity, profits and investments. Our key-finding is that operative profits were remarkably stable before and after divestiture, and that privatisation had no discernible impact on productivity trends. Major changes were however related to variations in financial arrangements and regulatory pressure.