Most scams calls come from abroad, paticularly from India (and from China in the case of the USA). In India it is an industry, with large "call centres" employing numerous agents. During scam calls you can often hear other talkers in the background.
The agents first get jobs at legitimate call centres, outsourced by UK companies like BT. That way they get free (or rather paid) training on how to talk to UK "customers" and on the technical side - I have found some scam callers (the ones who say my phone is being disconnected) to be very knowledgable about the BT phone system.
The local Indian police are not interested. The scam centre is a good employer and earner for their community, and they probably get a cut, or at least their wives work there. One guy on the web (I forget the link), an expert at networking, has a story that he delved and found not only the street address of one of these centres, but also the names of the bosses. He gave this info to the Indian police but they did nothing.