APN commonly refers to an “accelerated payment notice” in UK tax practice. It is a statutory notice issued by HM Revenue & Customs (HMRC) under Finance Act 2014 requiring upfront payment of disputed tax, usually in relation to tax avoidance schemes, before the substantive dispute is finally resolved. An APN is not a tax assessment but a payment mechanism. It can be issued where the taxpayer has used arrangements subject to a DOTAS (Disclosure of Tax Avoidance Schemes) reference number, a follower notice, or GAAR-related rules. The amount demanded reflects HMRC’s view of the tax at stake. Strict statutory time limits apply to representations against an APN, but there is no right of appeal to the tax tribunal against the notice itself; disputes typically focus on judicial review grounds (legality, rationality, procedural fairness). Accelerated payment notices are specific to the UK (England & Wales, Scotland and Northern Ireland) and do not exist in Irish tax legislation, where Revenue uses different collection powers. In UK tax litigation and advisory work, APNs are a key consideration in managing cash flow, settlement strategy and the risks of participating in avoidance arrangements.