The UK's National Health Service has introduced Social Prescribing initiatives to tackle loneliness and ill‐health, yet it lacks a theoretical foundation and evidence base for Social Prescribing's effectiveness. Recent research applies the Social Identity Approach to Health (SIAH) to explain Social Prescribing's health benefits, emphasising how social connection unlocks health‐enhancing psychological mechanisms. This systematic review therefore aims to assess UK‐based Social Prescribing programmes designed to boost social connection and alleviate loneliness, examining programme efficacy and the role of SIAH processes in health outcomes. Following PRISMA guidelines, a narrative synthesis of articles published from May 5, 2006 (when social prescribing was first introduced in the NHS), to April 8, 2024, was conducted, and their quality assessed using CONSORT‐SPI (2018). Of these programmes, 10 employed a mixed‐methods design, 8 qualitative and 1 quantitative service evaluation, totalling 3,298 participants. Results indicate that Social Prescribing's psychological value lies in quality rather than quantity of social connections, with meaningful connections fostering shared identity, perceived support and self‐efficacy, the latter of which sustains social engagement post‐programme. The SIAH was a useful tool for mapping mixed‐methods findings onto a common theoretical framework to highlight these key proponents. Overall, this review underscores the importance of SIAH‐informed Social Prescribing interventions in enhancing social connectedness, reducing loneliness, and promoting overall health. Please refer to the Supplementary Material section to find this article's Community and Social Impact Statement.