We needed an ambulance off road in the middle of Richmond Park where a postcode would also not help. We didn't have WTW either, which they asked for and would have helped immensely.
As I had a smartphone they did at least have a link I could click which would give me my w3w location, which I had to read back to them.
The problem is that w3w is privately owned and has multiple issues with it, as well documented elsewhere.
They could invest in a solution that allows for an OS grid reference to be discovered by sending you a link (a bit like they do with w3w), or some other open (already paid for) reference. That still has limitations if you don't have a smart phone with GPS on it, but I'd argue it's better than what they have right now.
Of course none of this solves for the fact the most useful location dataset in the country is the PAF, and we can't use that without spending a small fortune on licensing it.
e.g. 51.5010392, -0.1423616
7 decimal places of lat/lon is approximately a centimetre.
That kind of sanity was, of course, unacceptable to the rest of the world.
It's an ephemeral location for an ephemeral need.
When the ambulance arrives wave your hands and say "over here!". So they can do the "last several meters" of navigation by homing on your visual presence.
In the context of navigation that is good enough - if you are within 100 meters you can look to see your destination.