✒ Explanation by Jim Harra, Head of HM Revenue & Customs:

“Carelessness is a concept in tax law, it can be relevant to whether someone is liable for a penalty for an error in their tax affairs.

There are no penalties for innocent errors in their tax affairs — so if you take reasonable care but nevertheless make a mistake, whilst you will be liable for the tax and for interest if it is paid late, you would not be liable for a penalty.

But if your error was as a result of carelessness then legislation says a penalty could be applied in those circumstances.”