In the UK the quality of the electrical supply system is controled by the National Grid. The National Grid company has a set of standards that it refers to as the grid code. The code is the minimum standard of power quality that a generator supplies to the grid. If the generation does not meet the code it does not go onto the grid.
The code also sets standards for customers equipment if the running of the equipment can be reflected back to the grid. You would not want a factory with a large direct online motor depressing the local supply voltage everytime it is started.