Cycle helmets--when is legislation justified?

The issue of mandatory cycle helmets is highly contentious. The aim of this paper is not to argue for or against legislation but to suggest criteria on which the debate should focus. This is done by attempting to answer the question: 'What criteria must be met before cycle helmet wearing is enforced?' Consideration is given to principles, precedents and consequences and four criteria are suggested. The criteria are to do with effectiveness, personal liberty, public acceptability and the promotion of the public health benefits of cycling.