It was Sir Patrick Vallance who said it, @Fyoosh posted it up:
“Our aim is to try and reduce the peak, broaden the peak, not suppress it completely; also, because the vast majority of people get a mild illness, to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission, at the same time we protect those who are most vulnerable to it.” — Sir Patrick Vallance.
Thanks for finding this.
It looks like it's gone from "this is some kind of herd immunity" as a consequence of our actions to "we are planning on herd immunity as our only plan".
It was Sir Patrick Vallance who said it, @Fyoosh posted it up: