What are the cashflow implications of Self Assessment for income and corporation tax?

Background

Research would consider the challenges and opportunities for taxpayers and HMRC of more accurately forecasting end-of-year liability and collecting Self Assessment income (including corporation tax Self Assessment (CTSA) for smaller companies) closer to the point of income arising (developing our understanding beyond the Timely Payment Call for Evidence Summary of Responses, 2021). Opportunities for taxpayers include improved customer service (through digital self-service, near-accurate tax forecasting tools and earlier payment of tax, all of which support taxpayers to budget more effectively). Opportunities for HMRC include reduced error and supporting more taxpayers to pay on time, both of which contribute to closing the tax gap, one of Exchequer Secretary to the Treasury’s key priorities for HMRC.
Research objectives would include (but are not limited to): how HMRC can design policies, processes and services which support earlier payment; the cashflow implications for taxpayers and HMRC of moving to earlier payments and insight to ensure timely payment policy development considers (and looks to meet) the needs of financially vulnerable taxpayers. In this context financially vulnerable taxpayers are those on low-incomes or who have (or are at risk of falling into) tax debt.