Incidently if the observed R0 with no restrictions is quite close to 1 then "Herd Immunity" may actually be near at hand.Maybe, but Whitty always talks about Winter cases being worse for any bronchial viral infection due to higher viral load and bacterial infections occurring on top
Delta us so infectious (Natural R0=5) that it outcompetes other variants and it's antibodies prevent infection with other variants. Only a variant which eludes Delta antibodies has a chance of outcompeting Delta
I personally don't think this is the case as declining vaccination immunity will keep the case numbers going at a fairly consistent level for quite some time.
At current rates though, In a months time, most school kids between 4 and 18 will probably have caught Covid.