Hiya Geek
Do you have a picture of it?
Typically, if they own the home, then within reason, they can put up a fence around their boundary, no problem. Is it a decorative fence or is it a 6ft high sold wall type thing?
One place you can check is with your local council. They are the ones who set planning rules and who need to be asked for permission to put up any solid structures.
You'll also be able to find all the planning permission requests on their website directly, and see if they have been approved or declined, appealed and revised etc.
Would be interested to see a pic of this fence...