Minor Amendments were insignificant variation in a detail and details of an Planning permission which would not raise any new issues which would warrant the submission of a fresh Planning application.
They would allow for small changes to be made often as a result of modifications arising for practical reasons during the course of construction.
Many local authorities had established protocols for dealing with such amendments.
The legal basis upon which this is allowed has recently been challenged in Case law.
Notably:-
References
Minor amendment (UK Planning) Wikipedia(Text) CC BY-SA