Righto. Found a couple of things.
QH only has one part number listed for all metro's, QR1823S.
But first line has two:
80-90
http://www.firstline.co.uk/op3/f_ste...%20Rover&mmeid[0]=3736&mmeid[1]=3737&model=Metro&variant=-&subvariant=(1980-90)&engine=&product=Steering&var_desc[0]=3736__3996&var_desc[1]=3737__3997
90-95
http://www.firstline.co.uk/op3/f_ste...oduct=Steering
The difference being, the earlier metro ones are imperial, the later metic as per John's post above.
I've guessing I have the wrong firstline part.