If you completed a self-assessment return last year, you need to continue to complete a self-assessment return annually.
However if you are issued with a notice to file a tax return and you do not consider you need to complete one, because, for example, your tax affairs are no longer complicated, you can phone HMRC and ask for the tax return to be withdrawn and for you to be removed from self-assessment in the future.
But if you are issued with a notice to file a tax return, you have a legal obligation to complete one.