When a company contemplates a merger, when it’s the subject of a dawn raid, or when it needs to devise a compliance programme, competition law advisors are never far from the scene. Those advisors may be a formidable team from a storied City firm. But working alongside any group of external antitrust advisers are their essential in-house counterparts. Each side brings its own specialist skills and expertise to the table, but with costs, policy agendas and ever-changing legal frameworks to contend with, professional relationships are frequently put to the test. Rachel Bull investigates