These are tax returns issued by HM Revenue & Customs (HMRC) for completion by UK tax payers. The regime was introduced in 1997, with the idea of simplifying the UK tax system and it is certainly debatable if this has been achieved!
Who needs to file a return?
For the majority of UK individuals their income is taxed at source, such as employment income which is taxed under the PAYE system. Therefore, most people will not normally need to file a Self-assessment tax return. However, if there is any income or gains that is either untaxed or there is additional tax due, then it is the individuals responsibility to notify HMRC. Usually in all circumstances if HMRC issue a Self-assessment tax return then it must be completed and filed. Below are a number of examples where there is normally a requirement to file a tax return (please note that this list is not intended to be comprehensive):