'Most UK car manufacturers went fully over to metric fitting in the 70s . . .'

I would have to disagree respectively about this. In my experience working on my cars and those of others (81 4/4 SAE, 80, 85, 86, 89, 90 Plus 8s all SAE??) Only metric is occasional missmatched fitting.

Cheers,

Mark

1934 SS MX4
1938 Series 1 DHC
1951 Plus 4
2005 Roadster