Among the more reliable guides to the real prevalence of COVID-19 are the data collected on antibodies acquired following infection (measured as N-antibody levels, in contrast to S-antibody levels, which are acquired from both infection and vaccination).
Below is the latest graph from the UKHSA showing how antibody levels in blood donors in England have changed since autumn 2020.
From this and earlier UKHSA/PHE reports we can infer that the first wave infected around 5.7% of the population (though data from this period is mixed, with some showing up to 8.3%), the Alpha wave infected around 9.9% (perhaps a bit less if you use a higher first wave estimate – either way the first two waves together infected around 16%), the Delta wave infected around 8% and the Omicron wave has infected around 21.4% (so far). On these data, around 45% of the country have now been infected at least once at some point during the four Covid waves. Note this doesn’t allow for any waning of infection-acquired antibodies, which would mean these are lower-bound estimates.