It is your duty to be aware of your legal obligations when you run a business whether it is via self-employment or running a limited company. HMRC may communicate with you that you need to submit a tax return but it may not be via letters. They can notify you in an email. Not receiving any communication from HMRC, doesn’t mean you are not required to submit a tax return. And if you just started a business, HMRC may not know about it and won’t send you any communication. This also doesn’t mean you don’t have to file a tax return. If you aren’t sure whether you need to submit a tax return to HMRC, talk to a professional accountant.