Dave,
Thank you, that looks very promising. I didn't see "Whitform" on their website.
Do I take it that this is a true Whitworth thread form not some made up type of thing, and that these are so named because they don't fit the "official Whitworth" charts? There seems to be no technical description, it's probably so blindingly obvious that everyone understands but me. I can live with the price, didn't think it too bad at all.
Eug