There have been a handful of Denzel puzzles before but I don't think any of them have been the same as this car.
I wonder if this was a very early prototype, although it doesn't look identical to pictures on the web of some of the earliest ones to me.
I'll leave it for the moment, but I think Denzels should have a model name as well, e.g. 1500 S or Super 1300. I did find one which was supposed to be a prototype named the WD Super Sports, which was shown at Geneva in 1953, but it wasn't the same as the puzzle car. In fact I haven't found another one with that small lid to access the front compartment..
Maybe Wendax can throw some light on it?