Looking at that Racal Recorder voice recorder, say your average person speaks for 15 minutes a day on the phone, and there are 12 awake hours in the day when people call, that's 1,382,400 people's conversations that can be recorded.
i.e. 60 of those buggers is all that's needed now to record everyones conversations in the UK.
Ahh but it can only record 280,000 channel hours, which I guess means 580 hours per channel, or 24 days worth before the data needs moved off the recorder onto a file system.
Ahh the march of technology, Privacy Rights need to maintain-capability against intrusive surveillance by overzealous political-appointee-run departments of state.