Benefits only accrue when Heathrow is Cat III and ATC has managed to get two or more BA 320s in trail.
That shouldn't be a problem for ATC. In LVPs we have four full stacks of aircraft to chose from and we already work to the most efficient landing order rather than 'first come first served' when busy. I see no reason why we can't bunch BA 320s in the same way we bunch heavies or 757s at the moment.