Mechanically it was sound and it was not leaking light though the concertina leather cover, but the lens did not look right. On closer inspection it had light grey markings all over the outer and middle lenses (it has 3 lenses). A little googling later revealed it was fungus!
I tried all the normal things: lens cleaner, lens cleaner with a little rubbing, then a lot of rubbing. I tried alcohol (ethanol then acetone) but no success. Back to google and I found out that I needed Hydrogen Peroxide (hair bleach). I bought some 6% Hydrogen Peroxide from the chemists and dipped the lenses in the solution. It was a miracle. The fungus dissolves off in minutes and I was lucky not to have had a fungus that left marks on the lenses.
The lenses were very easy to remove with a precision flat head screwdriver onto the zoom dial and by prying out the retaining circlip. Just remember the orientation of the lenses as they are not symmetrical.
I put a Rollei CN200 colour film in, took some photos in the Northumberland hills and developed them. The camera worked and took some decent photos, but only with ample light. I struggled to focus on closer objects, probably because the markings are in feet and I'm far too young to think of feet as anything other then something with toes on them. Here are those photos:
