Interesting find on our travels, but as some may well know – the Spectrum version of S.T.U.N Runner wasnt particularly great (Well, the C64 version was only marginally better, but thats not saying much).
However, things could have been a whole lot better it seems, and the postage stamp sized play area could well have been extended. Check out the preview shots here:
Then compare to the released game shots here:
A rather different game from the looks of things. Was it merely a set of mockups (Like with what happened to Nemesis on the Spectrum), or was it an earlier version that was canned? One for a bit more research I think