Background Financial difficulties can precipitate and perpetuate mental health problems and are a predictor of chronic physical illness. The COVID-19 pandemic is an unprecedented public health crisis with profound health and socioeconomic impacts and the long-term consequences are yet to be seen. The poorest and most vulnerable groups are worst affected, further widening the health inequality gap. It is known that there is low uptake of universal and means-tested benefits in some communities. Various schemes have been put in place to improve uptake of benefits by co-locating welfare advice within health services. However, we need more research on how to do this most effectively to reach the populations most in need and to assess its impact on health, social and financial outcomes.

Methods We conducted a critical systematic narrative synthesis review of relevant papers published between 2010–2020 using an evidence-led framework described by Rodgers et al. consisting of four elements used to characterise the approach: developing a theory; developing a preliminary synthesis; exploring relationships within and between studies; and assessing the robustness of the evidence.

Results In total, 16,625 participants accessed and were supported by the welfare services, with £19,576,223 successfully claimed as one-off payments for participants. Participants benefitted from an additional £2,757 household income per annum and improved financial literacy. The services across this review generated an average of £21.95 of social, economic and environmental return on investment per £1 invested. Co-located welfare advice services actively incorporate elements of proportionate universalism and target those who are most at need of this support and who would not otherwise access the services. The services raised the profile of the importance and value of addressing social determinants of health with healthcare professionals and policy makers and de-stigmatising access to welfare services and being in receipt of benefits. Access to welfare services also produced demonstratable cost savings for the NHS. Welfare services facilitated more appropriate use of NHS resources, promoting access for those who needed it but were not accessing it and reducing the burden of welfare issues on healthcare practitioner’s time.

Discussion Overall, this review demonstrates significant financial gains for participants and for the first time demonstrates wider welfare benefits to participants, including access to housing, food, transport and employment. This contributes to the theory that these welfare services both directly and indirectly address social determinants of health thereby improving health and wellbeing and reducing health inequalities.