This paper aims to present a critical analysis of the Year 1 Phonics Screening Check (PSC), with special focus on the relationship between the UK Department for Education's policy-making and the evidence considered in the process of developing and evaluating the PSC. The reports from the in-house Standards and Testing Agency and from commissioned external organisations with limited remits have been analysed, with emphasis on how the screening check findings have been used in DfE decision-making. My conclusion is that the department has overestimated both the validity and the reliability of the check: partly because important sources of measurement error have not been explored, and partly because the available evidence has not been analysed in sufficient depth--or perhaps simply been ignored by the department. The whole phonics screening check seems to be the product of policy-based evidence, rather than evidence-based policy-making. This has, in my view, seriously undermined the value of the PSC as a screening instrument, and one must wonder whether it is "fit for purpose."