There are no penalties for "innocent" tax errors, the boss of HM Revenue & Customs has said.
Jim Harra's comments to MPs come amid pressure on ex-chancellor Nadhim Zahawi after it emerged he paid a penalty to the tax authority.
The Tory chairman faces an inquiry into his conduct by the PM's ethics adviser.
Mr Harra stressed he could not comment on individual cases, but said penalties were not applied when someone had taken "reasonable care".
Mr Zahawi has said the tax authority accepted the error over previously-unpaid tax was "careless and not deliberate".
He has given permission to HMRC to share details of his taxes with the investigation into his conduct, with his allies saying he believes this will back up his version of events.
Permission
Individuals must give permission for such details to be disclosed, because of taxpayer confidentiality.
Mr Harra, the chief executive of HMRC, gave evidence to the Commons Public Accounts Committee about managing tax compliance following the pandemic.
The MPs also quizzed him about Mr Zahawi's tax arrangements.
He said he would not comment on specific individuals, but added: "There are no penalties for innocent errors in your 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's paid late, you would not be liable for a penalty.
"But if your error was as a result of carelessness, then legislation says that a penalty could apply in those circumstances."
The BBC understands Mr Zahawi resolved a multi-million pound dispute with HMRC last year, when he was chancellor.
Tax
According to the Guardian, he paid the tax he had owed, as well as a 30% penalty, with the total settlement amounting to £4.8million.
The tax was related to a shareholding in YouGov, the polling company he co-founded in 2000 before he became an MP.
Earlier this week, Prime Minister Rishi Sunak asked his independent ethics adviser, Sir Laurie Magnus, to look into whether Mr Zahawi broke ministerial rules over the issue.
- Nearly 400,000 self-employed people on low incomes are being penalised for filing their tax returns late when most of them don't owe any tax.
Penalties can build up until people owe thousands of pounds, according to Tax Policy Associates.
The BBC says the non-profit group called for penalties to be cancelled if HMRC finds people have no taxable income.
HMRC said new rules would mean people who sometimes miss a filing deadline would not be penalised.