The change took effect on October 27, 1986, when rules that had stood for a century were stripped away in a single day. Fixed fees on share trades ended, and the line between the firms that took orders and the firms that dealt for themselves was erased. The City had not seen a day like it. Clerks trained for months to learn the new screens.
The cause was pressure. London was losing business to New York and Tokyo, and the old club of family houses could not match the size of foreign banks, so the government opened the market to outside owners and Wall Street firms bought into the Square Mile. The money flowed in. Old firms merged or vanished within a year.
The effect was swift. Computers replaced the open outcry on the floor, and dealing sped up while costs fell for big clients. The old lunchtime and the gentlemanly code gave way to a harder, faster trade. The skyline filled with towers. The jobs paid more. Graduates flocked to the dealing rooms.
London became a hub rivals had to chase. The Big Bang drew talent and capital from across the world, and it set the template for markets that trade by screen. The change also brought risks that later crashes would expose. The City has not looked back. The reforms spread to other markets in Europe.