Using a structural model of the interactions between governments, firms and insurance companies, we characterise the distortions in environmental liability sharing between firms and insurance companies that the imperfect implementation of government policies implies. These distortions stem from three factors: the presence of moral hazard, the non congruence between firms/insurers objectives and social welfare, and the courts' imperfect assessment of safety care levels exerted by firms. We characterize cases where the efficient liability sharing factor is above or below its full information perfect implementation level. We derive comparative statics results indicating how sensitive the liability sharing factor is to changes in parameters (parameters that underlie the firm profit level and volatility, the cost of safety care, the monitoring cost, the social cost of public funds, the effectiveness of care in reducing the probability of accident) that are relevant for the characterization of optimal policies (liability sharing, safety care standards) toward environmental protection or the prevention of industrial accidents. We derive policy implications regarding environmental disaster insurance policies.