It was to my great surprise to learn that rules of the census in UK are much more strict than in Russia. In fact, I pretty much expected the opposite.
To start with, one have no right to refuse the participation (and if they do, £1000 fine applies along with a criminal record). Also, the only question which is allowed to skip is about religion (and numerous other ones are mandatory). On the bright side, there is at last an option for atheists ("No religion") while the closest match in similar questionnaires (e.g. in NHS survey) is "None of the stated".
Another difference from the Russian version is that the information needs to be provided not only on people themselves but also on their guests stayed in their house on the particular date (actually, the census results are supposed to be a snapshot of country's life for a certain day catching internal migration details as well).
However, we can't yet fill in our forms. Of course, the whole thing could be done online but still is it necessary to get a personal code first by traditional mail to verify the physical address - and for some reasons our address is not in the list. Just as on many other government and corporate UK sites, it is impossible to enter any address you want - instead, you are given a list of available options upon entering your postcode. This is great for preventing the duplicated and misspelled inputs but when you're not in the database, you're in trouble. Issues like that are usually resolved over the phone, but we haven't managed to get thought the busy helpline yet.
There is a good chance, I suppose, that if the household is not in the database, it is impossible to verify the fact of participation. However, we're still going to act as the law expect us to, though that requirement was, as I already said, a surprise.