I would think that Whitworth sized nut and bolt heads on bicycles pretty much disappeared along with the older British manufacturers of components, like Williams, B. H., Chater Lea,etc. By the late sixties most components on British bikes were of Continental manufacture, and thus metric. Exceptions might be things like seat binders, or cotter nuts. I think most fasteners on Raleigh 3 speeds continued to be Whitworth until almost the end. As an aside, the British motorcycle industry was changing to Unified fasteners around 1969 or so, and cycle parts were often Unified while the engine and gearbox continued in Whitworth. Could be confusing! I believe that BSC bottom bracket, headset and freewheel threads became the ISO standard used almost universally today.
Regards,
Wes Gadd