| UPDATED: 22:19, Sat, Jan 30, 2021 Link copied Make the most of your money by signing up to our newsletter for FREE now SUBSCRIBE Invalid email When you subscribe we will use the information you provide to send you these newsletters. Sometimes they'll include recommendations for other related newsletters or services we offer. Our Privacy Notice explains more about how we use your data, and your rights. You can unsubscribe at any time. A Self Assessment tax return is a system for Her Majesty’s Revenue and Customs (HMRC) to collect Income Tax, and is used by millions. With this year’s deadline occurring on Sunday, January 31, 2021 at midnight, Britons will need to take action. However, Self Assessment can often be a complex process for some, and avoiding mistakes is key.