Many moons ago, I could have quoted chapter and verse on Whitworth and BSF hardware.
The short version is that Whitworth was the name of the English standard course thread. British Standard Fine (BSF) was the fine thread. During WW1 or 2, I forget which, BSF was standardized to US fine threads for compatability of war machinery, the only difference was the radius of the thread tip, otherwise they were interchangable.
The interesting feature was that wrenches were labeled according to the thread diameter and pitch. As an example, the same wrench would be labeled 1/4 Whitworth and 5/16 BSF, it would look like a 1/2 inch wrench because that was the size of the nut that fitted these two bolt sizes. Of course, it was not a 1/2 inch. it was some bastard size that Mr. Whitworth had figured out was the correct amount of metal to wrap around that size bolt with that thread. To the best of my recollection, there were no standard wrenches (labeled in England as AF meaning the distance Accross the Flats) which would fit Whitworth and BSF nuts.
Then there was the BA or British Association series which were used mostly for electrical equipment and was similar to the US numbered small bolt standard. Of course this did not have standard size nuts either, you had to use BA wrenches.
And you wonder why the empire collapsed. : )
For future reference, what you call the English system is actually American. England never had anything this rational.