My thanks go to Jonathan Petch for these rather fascinating photos of a Reliant Robin with a difference. (The single wheel being at the rear). Jonathan writes that it was:
... built by
the head of engineering of Reliant UK and it has a super sport engine and goes like a beast, it's all Reliant [Robin] baby. I am trying to sell it or swap it.
Jonathan can be contacted at: firstname.lastname@example.org