I have not had a chance to check it, but they have had a few Chorus techs out there and have been sent a new router and have tried many options to no avail...
They have an alarm, but they spoke to the company who said they don't monitor it (they are older and very non-tech so they would not have been sure). I am unsure if the Chorus tech has tried to disconnect the alarm, how dodgy the wiring is, or if it is even wired into the phone line for no reason, but I'm sure they know enough to test this.
It seems very strange that it is only at a certain time. I appears that they find it running again in the morning.