I can't help but wonder if they've got past the old storage issue that put this one on the back burner in 2011 after Francis Maude realized that the proposed aggregation of data would require IL6 storage (aka the same used by the spooks) to prevent national embarrassment, outrage and so on.
Anonymising data after it has been received is well and good, but you have to store the original data somewhere ... and last I checked, the cost of adequately securing the data was higher than the cost of the paper census.