In reply to: Can anyone describe the difference between a Pommie Whitworth and a US Whitworth? Is there any distinctive thing/things that show which is which?
The U.S. imports will be marked as such. You can see the Alexandria, Virginia import mark in my pictures. That may not be your question.
Try to get hold of Dugaboy1/MacD37 as he seems to have a fair bit of Whitworth lore.