I'm not a 777 pilot, but I've operated in/out of Heathrow for a couple of decades. I hope that my comments are allowed !
From day one I was told that accurate speed control (on pretty basic kit then) was
absolutely essential. Achieving this with the current equipment is simple. If flap is required, then lower some flap ! There's no excuse for this "plus or minus 10 kts" rumour either.
The LHR controllers are truly amazing, even allowing for the fact that they're "specialists". Lets not push it too far, despite their willingness.
If weight considerations mean that a required speed, most probably the "160 kt to 4d", is
not possible, then that obviously cannot be avoided, but the obvious course of action there is to tell a controller
well beforehand. If you're prevented from complying because of "Company regulations" then the Company, not LHR ATC, needs to change it's ways !
Two questions for 777 pilots -
[1] -- How much extra fuel is burnt, at (to be pessimistic) max landing weight, if flap is lowered to comply with the standard speeds (as achieved by everyone else) ?
[2] -- What is this burn as a percentage of typical total burn ?