Tesco plc (Tesco) has successfully challenged the Competition Commission's (CC) decision to recommend the inclusion of a new "competition test" in the planning system in order to address competition concerns in the groceries sector. The test aims to prevent large grocery stores obtaining planning permission for their construction or expansion where the local market is already highly concentrated and where the applicant has, or would have, a substantial part of the market. Tesco challenged the lawfulness of the test in the Competition Appeal Tribunal (CAT) on the grounds that the CC failed to properly consider certain matters which were relevant to its assessment of the competition test. Tesco's particular concerns related to the economic and welfare costs of the remedy and its effectiveness and proportionality. The CAT concluded that the CC did fail to properly consider certain relevant matters but the CAT's judgment does not preclude the possibility that the competition test could be lawfully recommended and implemented in the future.