There are a number of reasons why you may need to register with HMRC to submit a tax return. This could include:
And see HMRC's list of criteria to file set out below.
If you need to complete a tax return for the first time you should inform HMRC as soon as possible. The latest date that HMRC should be notified is by 5 October following the end of the tax year for which a return needs to be filed. For example, if you had income that necessitated you registering for Self Assessment in the 2018-19 tax year, you need to notify HMRC by 5 October 2019.
HMRC has published a check list of reasons that you may be required to submit a Self Assessment return. The list includes the following:
In certain limited circumstances HMRC can also ask you to complete tax returns for other reasons.
Uncertain if you need to register?
Please call with details of your various income sources in the UK if you would like help to decide, if you do need to register for Self-Assessment and/or with the completion and filing of your return.