eddiecat78
It's been available on findmypast for a long time. If you haven't subscribed before you could possibly do a freetrial
Based on something I read a few months ago, that probably means that findmypast is the 'body' (sorry, can't think of the right word there at this moment) that did all the work involved in making the 1921 censuses available online, and as a result was given exclusive use of it for five years.
If I've got that wrong, hopefully someone will give the correct explanation soon.
I have persevered with it on Ancestry this afternoon (had to click many times on some before some would load), and have already found some really useful info via these 1921 censuses.