I wrote the reply about infection rates in haste, I was in the middle of something else and not reading the article properly. That was the wrong answer to your question.
The study was based on local authority and GP figures. The doctor leading the study said "the figures are not perfect, with the number of severely ill patients as a proportion of the total cases being used as a marker for estimates of wider infection". The study claimed that assumptions were made including how long it takes for an infected person to become infectious to other people. Like all other models this one is flawed too. Remember Neil Ferguson's outrageous modelling which the government's early strategy was based on.
As I've said all along there will be huge differences in methodology and modelling, predictions etc. I find it all fascinating and because I don't trust the government figures (ONS) any more than any of the others as they are all best guesses, I have chosen to follow the various scientists who are bringing hope to the situation. My gut instinct is that the virus has spread through a considerable amount of the population and like I said when I entered this particular discussion point, if it hadn't we would be seeing a lot more spikes as people are rushing to get back to normal and that's not the case.
Just out of interest I checked the ONS site for the weekly Covid roundup. One of the things they have published today is that 67% of adults in Great Britain are worried about the effect of Covid19 on their life.
They achieved this figure from collating the survey answers from 1,424 individuals and weighting the results to be 'a nationally representative sample for Great Britain'.