Corporation of the City of London
In addressing the 'square mile' concept Londonist has provided a potted history of the City of London.
Worth noting that there are at least two plaques erected by the Corporation outside the City of London, both for William Blake: South Molton Street and SE1. Conversely Londonist points out that there is only one official blue plaque in the City, and it's not blue.
2021: Art Review published a major article entitled "London’s ‘Square Mile’ Is One Big Monument To Slavery". This summarises the status of the City's own Findings and Recommendations of the Tackling Racism Taskforce, and provides a list: "Some of the problematic memorials in the City of London and the individuals and organisations they celebrate not yet addressed by the City’s Taskforce On Racism."