Are you obliged to answer that question?
They may be obliged to ask it.
( Lord Gnome, Thu 28 Aug 2008, 13:36, archived)

course not
same as you aren't obliged to fill in your ethnicity, religious views, etc. But it's hardly a secret and if they think they can do something useful with it, good luck toy them.
( the mighty badger Aphrodite, on a bar stool, by your side, Thu 28 Aug 2008, 13:39, archived)

My guess is
That it gives the Office of National Statistics a reason to validate its budget as much as anything else- particularly when it comes to voluntary activities. I can see the point as regards employment as a way of measuring the effects of equal employment legislation, however I think there is a misconception about that too; namely that equal employment legislation merely states that it is illegal to discriminate against people on certain bases and does not actually set quotas which is the way it's often seen.
( Lord Gnome, Thu 28 Aug 2008, 13:46, archived)