Theoretically it is possibly. It could be achieved if there's no social contact. Everyone stays at home, don't mix and the very few out all strictly social distance then the percentage needed to have herd immunity would be low. (Because it can't be transmitted if there's no one to transmit it to!!) However, that simply can't occur as people can't all stay at home and maintain their lives.
Herd immunity (without a vaccine) can only if the immune response, gained after a person has had Covid-19, prevents them from picking up and transmitting the virus. It's not known if that is the case with Covid19. (This ignores the morality of the "collateral damage".)
Unfortunately, the first thing Johnson et al sold to the UK public as the solution was herb immunity, and to achieve it you go out and mingle (unless you are vunrable) So huge about of people believe this is scientific fact. Add to that it quite obviously far more appealing to think you're solving the situation by socialising! It's very difficult to unlearn people.
Fact is herd immunity is achieved through vaccination, and a decent uptake of that too.
Well, that's my understanding anyway. Maybe Im wrong, but sadly the OP hasn't come back and provided the link that shows WHO thinks it's the way forward (and why).
I could provide lots of links that support what I've just written though!!