There were some long-wheelbase versions made as limousines, funeral cars etc. That would explain the colour.
The Furious Driving YouTube channel has a video of one:
Apparently it's the only one left in the UK so if it was this one you saw, it's a lucky spot - it's the right age.
Fancy that! I’m fairly sure that is indeed the one. I was in Letchworth when I saw it (where that video was filmed).




( That's the sort of thing I'd do... )





