Corporation Tax self-assessment (CTSA): Assessments: Discovery - information available - prevailing practice
FA98/SCH18/PARA45 does not allow you to make a discovery assessment when:
- the loss of tax or incorrect statement of an amount is attributable to a mistake in the return concerning the basis on which the company’s liability ought to have been computed, and
- the company made the return on the basis or in accordance with the practice generally prevailing at the time.
So, you cannot make discovery assessments simply because the Revenue have changed their practice in relation to the treatment of a particular item.
A company objecting that you have not complied with the conditions of FA98/SCH18/PARA43 - 45 when making an assessment must make its objections in an appeal against it.