meic wrote: ...I still think that they think in boxes that a good many of us do not fit into. ...
The computerised data collection can only reinforce that. Boxes spawn boxes.
They are also going in ever decreasing circles trying to avoid treading on toes - the nationality questions being an example. FWIW, I'm a British Subject by birth. It seems to me that if they want to know about nationality they need that level of accuracy or it's pointless. The questions as currently posed suggest a greater interest in nationalism than nationality, but I imagine they were just worded like that to antagonise as few respondents as possible.
It's an exercise for its own sake, a relic of an earlier, less sophisticated era, which nobody has the bottle to put out of its misery. IMO.
Who writes this garbage? 
Anybody can conduct an interview under caution - it's a restriction on those in authority to protect the individual, not a power. The big test is what happens if somebody won't stand still long enough for the caution to be administered and the questions posed. That's when a power of arrest can come in handy.