The White Rabbit in Wonderland was worried about being late. You should be too, when it comes to your tax return.
If HMRC has told you to file a tax return you must do so by 31 October for a paper form, or by 31 January for online filing. If you miss either deadline you will get a £100 penalty. This penalty applies even if you have no tax to pay, or are due a tax repayment, for the year the return covers.
The penalties increase substantially if you are 3 or 6 months late with the return, and there are penalties and interest for paying late. A ‘reasonable excuse’ will get you out of penalties, but HMRC won’t be sympathetic to any old sob story. The taxman enforces such charges without mercy as another way of raising revenue. It’s much better to know what you need to do and to do it in good time.