If Smiley had answered Vladimir's phone call...
Suppose Smiley had been visiting the Circus when the General made his phone call.
"Mr. Smiley, this is Mostyn in Oddbins. There's a phone call for you."
Do you think it would have affected the outcome?
I think that Smiley would have instinctively recognized the danger, and quickly improvised a safer meeting procedure. But it would have been too late, and the result would have been the same.