The extraordinary success of the Scottish beer and bars company BrewDog owes much to a shrewd realisation on the part of its co-founder, James Watt. The 42-year-old, who announced his departure as chief executive on Wednesday, realised early on that punk, once a subculture, could be turned into a lucrative marketing brand. Under Watt, and his co-founder Martin Dickie, BrewDog styled itself as an abrasive upstart on a mission to upset Big Beer and, in his own words, “set fire to the scene”. Its cornerstone product was christened Punk IPA, while the crowdfunders who supplied much of its early-stage investment were given the soubriquet “Equity Punks” and invited to rowdy annual meetings that resembled rock festivals rather than an investors’ gathering. Along the way, Watt revelled in his role as the snarling public face of BrewDog, while Dickie took a back seat. Watt gleefully lashed out at anyone who BrewDog did not consider “punk”, often as part of the company’s frequent, sometimes near-the-knuckle publicity stunts. The Scot, who comes from a successful east coast fishing family, threw taxidermy cats out of a helicopter above the City of London, a clunky reference to the financial district’s fat cats. He and Dickie...