Coal Tax Posts

In 1605 the Corporation of the City of London started raising funds by weighing the amount of coal brought into the Port of London.
It was decided to increase the amount raised following the Great Fire of London in 1666. Much of this extra money was spent on rebuilding St. Paul's.
With the development of rail and canal transport during the 19th Century, the boundary was changed to a 20 mile radius around London and approximately 50 posts were erected. Although duties were not collected at these points, they were there to show where an individual would be liable.
In 1861 the catchment area was reduced to the Metropolitan Police District. At this point there were about 280 posts installed. The vast majority of these still remain. In 1889 when the London County Council was formed an Act was passed to abolish the duties.  
I've now seen two of these on Epsom Downs. The figures and letters on the marker relate to the Acts of Parliament and the reigning monarch at the time.