Andy Hall wrote:

If the manufacturers intended their meters to run as a design goal at
50% over stated capacity, they would rate them that way.
Alternatively, they would manufacture them down to the stated spec.
with much less headroom and more cheaply.

If there is overdesign on the part of the manufacturers it is for
reasons of a safety or accuracy purpose.

This doesn't sound right. In the 1970s the specification was set by the
gas boards engineers. All good engineers overspecify if they want a long
lifetime product. The manufacturers tested the product to a supervised
gas board standard, knowing that if it failed, they would lose the
business. These were the days when products were properly tested for
reliability and products were rated on their lifetime cost as much as on
the ex works price. So IMM is probably right in saying that a gas meter
of his era would perform adequately with a 100% overload. Now that
IEC9000 defines the quality standard, the product is extremely likely to
be crap when it leaves the production line having been built for the
lowest possible cost and may not withstand the 100% overload which IMM
wishes to use. I wouldn't even bet that the modern meter would stay
working correctly when used at 100% load for a couple of years!
Certainly some modern semiconductor electricity meters have a very short
lifespan (12 months AIUI)

Regards
Capitol