Strength-5. There's been a final director at Heathrow for 40+ years but his task is primarily to achieve extremely accurate spacing and not to monitor the activities of traffic on the ILS, which he must assume will do the right thing. Quite obviously if someone wanders left/right or up/down then action will be taken but I don't think our "trappers" would approve the easier phraseology by putting the onus for maintaining the approach profile on the final director. Thankfully I can't remember the last time anyone did descend too low so may be our weird system works!