That’s completely at odds with what UCL actually said. Yes, they reckon the level of immunity generated by natural infection and vaccination could well be at a level that could be called herd immunity, but they also said that just opening the flood gates would then require the percentage of immunity to go higher in order to maintain herd immunity.
Their modelling is based on current data. Current data, obviously, is being collected during pretty strict lockdown measures. It incorporates the risk of catching the virus, the current R rate and of course the degree of immunity within the population. So, end restrictions, the R rate inevitable rises, as does the risk of infection, that in turn renders this particular model completely redundant.
Herd immunity can only truly be called when restrictions are completely gone and the R0 of the virus stays consistently below 1. Unfortunately, we’re still a bit away from that.