I think the ladder has landed somewhere in "The Land of Spiders" - under my desk/workbench - and hidden itself under one of the side cabinets in the dust and cobwebs !
No chance that I can get down there without re-arranging the room, as I'm too stiff and knackered to do so.
I've decided to bite the bullet and buy the resin twin-pack, as one of the ladders can be used on the Jag model, and the other adapted for a Mirage III model.