The Environment Agency are responsible for the regulation of radioactive substances in England, which is a highly controversial area to regulate due to the public perception regarding the associated environmental and health impacts. This is further complicated by the Environment Agency's primary aim of contributing towards sustainable development, which is another controversial and contested concept. The principles of good regulation require a proportionate approach, which can be considered a key component of sustainable development also. However, published literature asserts that the regulation of radioactive discharges is disproportionate, which lacks verifiable data on the regulatory compliance costs and impacts imposed. This also implies that the regulation may not contribute towards sustainable development, which is compounded by the ambiguity of this requirement in the regulatory framework. This thesis therefore seeks to evaluate whether the Environment Agency is achieving its primary aim of contributing towards sustainable development in its regulation of radioactive discharges. To this end, this study sought to identify the interpretation of sustainable development that the law, policy and guidance for the regulation of radioactive discharges requires the Environment Agency to adhere to, and then collect data to assess whether this is being implemented.To achieve this, the law, policy and guidance for the regulation of radioactive discharges has been mapped on to an enhanced sliding-scale of sustainable development interpretations. This has revealed that the regulatory framework drives the Environment Agency to adhere to the newly developed interpretation of stronger sustainability, which requires a proportionate approach to be applied within the limitations of the environment. The regulation applied to Sellafield's radioactive discharges has then been assessed against this stronger sustainability paradigm. The data collected confirms discharges are within environmental limits and that the regulation has resulted in direct compliance costs of £120 million between 2002 and 2009 without yielding any benefit to the environment in terms of a reduction in collective dose. The measured costs and benefits have been supplemented by a qualitative analysis of impacts that cannot be quantified, and these reinforce the contention that the regulatory approach at Sellafield is disproportionate and therefore inconsistent with stronger sustainability. A likely cause of the disproportionate regulatory approach is attributed to stakeholder and political pressures. Improvements have been proposed to address the disproportionate approach, which have already influenced the removal of some discharge limitations.