It seems to me that we are getting sidetracked from the original post - and I am guilty of that too.
It would appear that BA SOPs conflict with 160 to 4. This is an issue for BA to sort out, not ATC. If it requires 170 to 5 or whatever, then BA should push for it - moaning here will not do it. The rest of us can cope. In any case even an instant speed reduction from 160k to 150k at 5d instead of 4D makes, I think, a difference of about 200ft in separation - which is lost in the mists of Vref spread anyway.
The major issue is total non-compliance. Short of actually executing pilots like 411A, the only solution is for ATC to begin formal reporting. The on-board data recorders will show the companies whether it was so.