International accounting rules on the treatment of mergers and acquisitions are difficult and expensive to implement and result in disclosures that investors don’t want, according to a study from U.K corporate regulator the Financial Reporting Council.

The FRC said the International Financial Reporting Standard on business combinations was “poorly applied” because companies still didn’t understand its requirements and found its rules on valuing intangible assets—such as brands and customer relationships—were too complex.

The study also found that companies gave insufficient or inconsistent information about material acquisitions in their audited accounts when compared to the rationale for these acquisitions and supporting explanations given in their business reviews.

“A step change is needed in the quality of the information about M&A transactions given in annual reports and accounts,” said Ian Wright, director of corporate reporting at the FRC.

Companies are supposed to have been complying with the relevant standard, IFRS 3, Business Combinations, since 2004. The FRC reviewed compliance with the standard as part of a wider project to make company accounts less complex and more useful.