The stand ground markings are pretty clear at LHR, IMHO. The issue of stand guidance seems to be a combination of vested interests, inertia and finger pointing.
I, for one, would be quite happy to taxy onto stand as it is easy to see if anything is infringing or not. As it's still MY fault if we hit something, even if the stand is supposedly checked obstruction-free, I would welcome the POWER to taxi on there myself as I'm already taking the RESPONSIBILITY.
This has a parallel in the ATIS instructions: "Pilots are to exercise caution at the holding points as wingtip clearance may not be assured". If we all put the brakes on until we got a marshaller, both going onto stand and down near the runway, the penny might finally drop.