ABSTRACT Transparency is core to the principles of electoral oversight. The disclosure of information is designed to allow voters, the media, academics, and civil society to hold political actors to account. However, in the context of evolving campaign practice occasioned by the rise of digital technologies, the effectiveness of transparency mechanisms needs to be consistently scrutinized (Electoral Commission. (2018). Digital campaigning: increasing transparency for voters. Electoral Commission.). In this paper we examine a lauded system of electoral transparency – the UK's electoral finance regime (Power, S. (2020). Party funding and corruption. Palgrave MacMillan) – and evaluate its effectiveness. Analysing a unique dataset of 22,720 separate items of expenditure and 5,770 invoices recording campaign spending at the 2019 UK general election, we review the sufficiency of the process and content of existing transparency disclosures. Our findings show significant deficits in the system of electoral transparency. We find that UK parties are not reporting data consistently, meaning that invoices are regularly uninformative, and that existing reporting categories are unable to capture the full spectrum of electoral activity. These findings are significant for understanding the requirements of an effective disclosure regime, but also for questioning the utility of the disclosures available to voters.