If you know that you need to fill in a tax return for the year ended 5 April 2016, then you should have done something by the end of October 2016. This is either to submit a paper tax return, or to see an accountant. Carlisle accountants David Porthouse and Co can help here.
You need to submit a tax return if you were sent one by the Revenue, or if you had any income they don’t know about, or if you were self-employed at any time, or if you had any capital gains.