I bumped into someone at TFW security last month doing this, and wondered how it was implemented,

Now upon arrival back at LHR, is there a similar facility? I only have experience of T3 when escorting my father when using wheelchair assistance. On departure it wasn't too bad (except I had to get the lounge agent to call SA to pick us up from the lounge so we missed preboarding), but on the return, arrival back in to LHR T3, it took an hour an a half to get from the aircraft to landside, mainly due to multiple inefficiencies of the system, not least (a) a bizarre wheelchair transit area and (b) forcing us into the manual passport line rather than using the passport self-scan.

Having the opportunity to have access to a wheelchair at the arrival gate and wheel ourselves without the extended assistance delays would be very useful.

Many people are walking infirm, i.e. they are perfectly capable of walking short distances or standing for brief periods. It's walking or standing for extended periods that's the problem.