It's probably a debt collecting company.
Although the list, which Herc linked to, shows it as a call box, many call boxes have been removed and the numbers reallocated.
As I'm not worried about phoning any number that has an ordinary (rather than premium or international) STD code. so I've just done the easiest thing and dialled it.
The phone was answered straight away by a guy called Dean who was far keener to find out who I was than to tell me anything about himself or who he worked for. (I told him I was calling on behalf of a fictitious friend. I could hear him rummaging through his paperwork, looking for the name I gave). He did confirm that he was phoning from a company but stated that he had to speak to the correct person as the nature of the business was a 'personal matter'. All of that is perfectly consistent with the practices of debt collection agencies.
Chris