All council offices will operate differently, some will have just a procurement officer, some will have an entire office.
Its very difficult for anybody to answer, its simply a matter of asking the right questions until a light bulb goes off in somebody’s head on the other end of a phone.
All councils will have this facility its just finding out what they have called it and where it is, it could be embedded in a number of departments such as
Quantity surveyors
Street Cleansing
Borough Surveyors and/or Maintenance
HR and/or Procurement dept
Contracts and /or Facilities
Director of finance dept
etc etc
It may even be fragmented across departments based on type of service, or completely contracted out to an agency.
Just persevere and you WILL get there eventually. The question has to be “Who maintains the approved contractors list"?
The only alternative is if someone has already done the legwork with your particular council office and can advise.