It is inevitable that there will be cases in which a taxpayerʼs self-assessment will contain more than one error, each with a different cause and, more importantly, a different level of culpability.
Extra care needs to be taken in such cases to ensure that a discovery assessment does not go too far.
The historical approach
Historically, the approach was as typified in Hudson. There, it was held that once it has been shown that there had been (what is now) careless or deliberate conduct leading to an under-assessment, then HMRC are entitled to assess so as to correct all errors previously made by the taxpayer in relation to that tax year.