No first I've heard of Whitworth. Like you said modern vehicles are metric. It was the changeover where you had a combination of metric and SAE.
Google tells me:
"When did Whitworth stop being used?
Whitworth and BSF officially became obsolete in 1948 following an agreement between the UK, US, and Canada to standardise on the American UNC and UNF fasteners for future use."
So it's official, my spanners are museum pieces!