Windows GPS location completely wrong, grabbing my previous address?

Is your older computer turned on and if it is what location does it show. New one could be sharing info with old one. Just a thought.

My location is either taken from my phone's GPS or from a third party GPS database that associates my wifi, or several wifi's in a built up area, with the phone's GPS.

Try other mapping software like Bing Maps or Apple. My location was wrong for a year after I moved house. You could try changing the name (SSID) of your wifi to break the association.