What makes a merger? That’s the question being asked this week, after Norton Rose announced deals with Canada’s Ogilvy Renault and South African firm Deneys Reitz.

The combined business will rank as one of the world’s top 10 firms by headcount when the three-way tie-up takes effect next June, boasting more than 2,500 lawyers in 38 offices worldwide and gross revenue of over $1bn (£626m).