PAYE54190 | Employer returns: regulation 80 determinations: amendments on appeal
From HM Revenue & Customs · PAYE Manual
Sometimes after a determination has been made, new information may become available that shows the amount is either excessive or too little.
Once a determination has been made, it can only be varied upon appeal. There are only three situations when it can be amended
If the determination was not under appeal, it will have become final and determined so a further determination will need to be considered.