We analyze the simultaneous relationship between managerial ownership, board structure, and firm value, using a sample of all UK non-financial listed companies. We test the hypothesis that managers in the UK should become entrenched at a higher level of ownership compared to their US counterparts because of institutional differences across the two markets. We find a strong U-shaped relationship between the level of managerial ownership and the probability that the roles of chairman and CEO are split, that a non-executive director is appointed as chairman, and the proportion of non-executive directors on the board. However, we report a generally weak relationship between firm value and managerial ownership, board structure and the combination of managerial ownership and board structure. Our results cast doubt on the effectiveness of these internal corporate governance mechanisms.