My thinking was actually six-banded armadillo - quite apart from anything else, they are available readily in private hands and in public collections in Europe, whilst the nine-banded population is extremely low.
And having visited the collection today, observed both armadillos at some length (there being two of them) and - most importantly - spoken for some time to one of the keepers, I have a conclusive identification for the animals!
*drumroll*
They are large hairy armadillos! The low image quality distorted the shape of the animal in the photo somewhat - in person they were distinctly squatter than that photo made them seem.
They arrived from London Zoo in August, in case anyone is interested in their origin.