This article considers the supervisory jurisdiction of the UK courts through an examination of their control of the UK tax authorities. It concentrates on the conditions under which the tax authorities have been authorized by the UK courts to enter extra statutory arrangements to afford some taxpayers concessional treatment. The article considers the basis of judicial review and then examines the legislative framework within which the Revenue operates. With this background the article considers the principles of judicial review in tax cases. Starting with the general principles, it then examines the argument that the Revenue makes extra statutory concessions on the basis of its powers of care and management and it considers the limitations of that argument. The cases dealing with legitimate expectation are examined too, as are the limits on the legitimate expectation principle. Finally, the article considers “the slippery principle of equality” within the UK constitution and the equally frustrating (for third parties) problem of establishing locus standi. The article concludes that there are significant tensions between competing interests when the Courts review the Revenue’s granting of extra statutory concessions. They seem to have afforded the taxing authorities considerable autonomy in their fulfilment of their management function, but they have limited them to the exercise of discretion only in the course of their care and management of the tax system and in the context of their primary duty to collect tax. The author concludes that the courts have done well in balancing the interests of the tax authorities and taxpayer but that wider interests, such as equality between taxpayers, have not fared as well.