[Hanno Spoelstra]

Some info on Stewart & Ardern:
https://en.wikipedia.org/wiki/Cunard...art_and_Ardern

Looks they were still around in 1968:
http://archive.commercialmotor.com/a...rdern-stand-48

And could this be it today (a non-trading company, but still)?
http://www.allcompanies.co.uk/catego...roperties.html