Saying it 'It may well have said on the form that it was for census requirements' is simply not sufficient.
It has to be EXPLICIT otherwise it is not compliant.
The reason, is in part to ensure there is public trust in the collection of data and it is not being used for dubious reasons. The fact that government is currently working very hard to undermine that further because they are desperate to please a bunch of people with a nasty agenda doesn't help.
It only serves to make questions like the OP's legitimate even if she's 'goady' about it. Because what you interpret as 'goady' sure as hell looks like 'fear' to me and that is just not right regardless of how it is expressed. It undermines the fabric of a cohesive society.
There are people on this thread who have told the OP in quite passive aggressive terms why she must comply yet they are not being pulled on that yet the OP is pulled up on her tone and her manner. Why IS that?
This has to be about mutual understanding and a mutual appreciation about why someone might feel very fearful about giving that information.
This is why sensitive and appropriate handling of the issue is required from all institutions and people in positions of authority. (Yes that includes you Mrs Rudd and Mrs May) and why the public need to also be properly informed on why there is fear over data collection, because those who are doing it also in a position of power purely because they are British and much of the national press is behind them with this hysteria over immigration.
It has implications for how people interact with other services and other government institutions both in the short and long term.