This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Inheritance Tax Manual

Negligence: onus of proof

It is important to bear in mind that negligence may be wholly unintentional. You do notneed to show that there was intent to deliver an incorrect account, information ordocument. Similarly, an assertion by the taxpayer or his agent that there was no intentionwill not prevent your seeking a penalty.

The onus is on you to demonstrate that there has been negligence. You will normally dothis by showing that there has been an error or omission for which there is no knownacceptable explanation. The onus will then be on the taxpayer to demonstrate that theerror was entirely innocent (IHTM36311) and did not involvenegligence.