Examines, following the Supreme Court ruling in R. (on the application of DA) v Secretary of State for Work and Pensions, the use of the “manifestly without reasonable foundation” test in domestic judicial review challenges. The application of this benchmark in a series of human rights based challenges to social welfare reforms – such as the high profile “bedroom tax” and “benefit cap” policies – has been pivotal to their outcome. This paper argues that the application of the test is problematic as it is a formulation derived from the margin of appreciation doctrine and does not transpose to domestic application. In the alternative – even if it is the correct test to apply in some circumstances – it is to be applied far more flexibly than currently and that a “very weighty reasons” benchmark applies for some classes of discrimination.