As you can see from the edit dates, a lot happened here over the winter with traffic starting to return to normal in March, at which time, the stretch of The Pavement and Clapham High St that leads round to the Underground Station had been pedestrianised. However, looking at the final plan for the Regeneration Project, that was going to be reopened to traffic. When I was trying to find this information back in March, it didn't appear to be available. Perhaps I just entered the wrong search terms into Google
It's on my list of high priority places to visit, hopefully I'll get time next weekend, to understand what final changes, if any, have been made. Certainly, when I came through the junction at the A3/South Side, a left turn was possible, otherwise there was no way for traffic from the Old Town direction to get onto Clapham Park Rd, but if The Pavement/Clapham High St section has reopened to traffic, as indicated on the Final Plan, then that resolves that and I can understand the reimposition of the banned turn there.
I'll update it now to the Final Plan diagram and, hopefully, that's how it's been implemented.