They could.
But they won't as such a plug would be larger, more expensive and have no real use.
I have some of these. They aren't large, were cheaper than Duraplugs, and withstand rough handling.
View attachment 367092
So, either these people are wrong about the plugs taking 2.5mm.
Or they are wrong about it being manufactured to BS 1363.
Or Risteard is wrong.
Which is it.?