In the United Kingdom, government proposals for the introduction of an identity (ID) card have raised considerable privacy concerns. In the present research, opinions and attitudes about different ways of implementing ID cards are examined using an experimental methodology. Specifically, the level and type of compulsion and application process, and the use of a centralized database or trusted third party to hold personal information, are compared for attitudes towards ID cards. Moreover, the impact of implementation scenarios on people with different privacy concern profiles is examined. The results show that an implementation that combines high compulsion with a centralized database (the approach currently favoured by the UK Government) leads to the greatest negative shift in attitudes towards ID cards. Implementations proposed by others (e.g. the London School of Economics) show significantly less negative shift in attitudes. People’s pre-existing privacy concerns also influence their evaluation of the different implementation scenarios.