After exhaustive trials and a tongue transplant we have a new winner - the Thai Dragon. It's a 3-inch long tapering red chilli of such venom that one chilli can heat a four-person curry to near Vindaloo strength (9 on the Richterji Scale)
And it's a prolific cropper. One plant in our greenhouse looks like it's going to satisfy our chilli requirements for the next year. If not two.