RE: Correction to Self AssessmentFollow-up question: I submitted my Self Assessment on 31 January, but spotted a mistake now and need to amend my filing. This mistake doesn't affect the amount of tax I needed to pay. Will I face a £100 late filing penalty if: a. I amend my filing using Online Self Assessment, within 72 hours of initial submission? b. More than 72 hours has passed, and I contact HMRC to amend my filing?