As identified above, the system has been installed by Affiniti. There is one prefix beginning 01773 allocated to it and it is
01773 7301773 730199 has just been answered as "Derbyshire Police". Other nearby numbers ring and may also be suitable.
Others such as 730180 and 181 ring after a delay, so could be diverted to a mobile.
I found this number by calling 730100 which I found gives "The number you have dialled has not been recognised". 730200 on the other hand is NU (number unobtainable) - a single tone. This suggests to me that it (and nearby numbers) are infact allocated to a particular subscriber, probably as part of a DDI block of numbers (of which NU ones are not used by the subscriber), whereas "not recognised" is not allocated to any subscriber. I tried nearby numbers and hey presto!
At the bottom of Derbyshire Constabulary's
contact page it says:
Quote:Calls from overseas
An exclusive telephone number of 01773 730215 is provided for the exclusive use of overseas callers only.
Looking at the wording, I wouldn't put it past them if they screen calls and ensure that they are non-UK calls to this number.