Regardless of the regulatory style chosen (＇command and control＇ or ＇functional＇) a vital prerequisite for coherent safety regulation in the nuclear power industry is the ability to assess accident risk. In this paper we present a critical analysis of current techniques of probabilistic risk analysis applied in the industry, with particular regard to the problems of quantifying risks arising from, or exacerbated by, human risk and/or human error.