[David Simpson]

I remember, some time ago, when a similar thread query was raised, that I suggested the possibility of folk who own a NPL Standard Cell or Resistance taking them along to BVWS Swapmeets for folk to have their MM's & DMM's checked out calibration-wise. Also, if there are folk who own,(or can scrounge from work) a laboratory standard 2003N or Cropico Resistance Bridge, or similar Lab Grade equipment, they could take them along. There would be no issues, I suspect, with BVWS Officials, as they are purely battery operated.
50p or a quid a shot could go to the Museum or a chosen charity. Folk could then return to their UK locality, & their MM or DMM(along with its known accuracy, or discrepancy), could be used to check other VR enthusiast's test equipment nearby.
As David says - you don't need lab accuracy for testing vintage radios. They're full of 10% or 20% carbon resistors(old body/tip/spot) for example.
If folk are test equipment buffs, then maybe more accuracy is required. But then, take AVO CT160's & VCM's - their tabulations of voltage tolerances are laughable, for example.

Regards, David