Paul, I have researched this as thoroughly as time allows and all I can find is that Innocenti was sold to Leyland in the early 1970s (I hadn't known that before - Leyland certainly did nothing with the brand, sadly) and this van may well have been a Leyland attempt at an Innocenti delivery van, using, as other Innocenti vehicles did, Leyland engines and other sub-structure parts.
It's a lovely, clean design and I'm sad it never made it to the market. Mind you, it probably would have rusted to bits in no time, this era being one of the foremost for manufacturers creating rust-prone vehicles.
I hope this will garner me a point - I was getting to the end of my ideas as to what the van was and kept thinking, those
ARE BL wheels, so what else could possibly have had them? After the information as to its origins was confirmed, I just posted 'Innocenti', not expecting to be right at all!