This week, the City of London celebrates the 20th anniversary of "Big Bang" - the deregulation of markets in 1986 which ended fixed commissions and removed restrictions that required companies to be narrowly specialised and made new entry, especially by foreign businesses, substantially harder.

"Big Bang" was the result of legislation passed a decade earlier whose significance few people in the City then appreciated. The scope of the Restrictive Trade Practices Act was extended to services. That law did not ban agreements to restrict competition. It required those who made such agreements to place them on a public register. The register included a wide range of harmless practices, such as the official steps of the main Scottish country dances.