From the video, the manoeuvre seems to me to be elegantly executed. The flare attitude was held exactly, despite diminishing elevator authority, until the nose was lowered. There was no danger of a tail-strike at any time. The runway is long, and if ATC didn't need them to get off quickly because there was someone coming behind, they had no need for urgent speed reduction; rather the contrary, if this was 27R, as T5 is at the far end.
Contrary to SOPs, no doubt, and from what others are saying, maybe in BA's world that will get them shot, if only to discourage other pilots. But it's a pity, just the same. BA should be proud to have such a skilful pilot.