If anyone else has the same issue, the 1/8 BSF nipples arrived, they are much larger, than those currently fitted
The correct size for the stub axle grease point on a standard 1970's 4/4 is in fact 1/4 UNF as I originally thought.
I am now off in search of those!
Oops, sorry about that! I wonder when they changed - they are certainly 1/8 BSP on my 1986 car (you did get BSP not BSF, didn't you?)
You can get 1/4" UNF nipples from Vintage Motor Spares too, as per my original link.