The EU has published guidelines for the biggest overhaul of rules governing mergers since 2004. However, commentators are warning that loosening the M&A code may create new risks and still not deliver the “mega companies” that proponents seek. And EU officials appear divided. Where does this leave compliance teams?

Ruth Prickett graduated from Cambridge University with a BA hons in History and has specialized in business and finance journalism for the past 20 years. She was editor of Financial Management, the magazine...