The most recent research seems to suggest there won’t be any type of herd immunity. As plenty have been saying since the beginning, this is a coronavirus - and in all likelihood it will therefore behave just like other coronaviruses with which we are more familiar.
So, we need a vaccine to give some form of protection to the most vulnerable. Without that life can’t return to normal.
On another lockdown, I think there will be growing pressure on that front over the next fortnight. We are already at an average of 200 daily deaths, quite some way ahead of the predictions made by the scientists a month ago when they said we wouldn’t hit that figure until mid-November (and, at the time, they painted that as a worst-case scenario).
The NHS is likely to start to really struggle before too much longer. That - and the desperation to salvage some kind of Christmas - may force the government into a two or three week national circuit break; although I’m sure they’ll be keen to dress it up under some other name.