Breakingviews: Return of the stock jobber

Big Bang is coming undone. The major investment banks are starting to unpick the full-service equity operations they have built up over the past two decades.

Few have yet made their intentions explicit. But it is possible to get a sense of where things are headed from HSBC's recent announcement about its equity business. The international banking group said it was scaling back agency brokerage in order to focus on the trading side of the business. It is not alone in heading down this route.

It isn't clear what will take the place of the full-service big players. But the market's new structure might bear more than a passing resemblance to the one the City abandoned in 1986.

Before Big Bang, the stock exchange operated on what was called a single-capacity system. That separated traders – known as "jobbers", who provided liquidity to the market – from "brokers", who bought...