"Low UK sales are put down to the lack of a diesel engine"
Previous Imprezas sold for their performance, and typically if you're after a performance car you buy one which runs on petrol. Diesels are for rep-mobiles and shopping carts.
Poor UK sales are because the new Impreza is a damp squid. To make excuses for a lackluster offering from Subaru does them a disservice.
The only question is why didn't Subaru learn from the quickly modified google-eyed model?
The only move that Subaru can do with this car is to reduce the price. Increasing the STi by £ 1,600 after getting mediocre reviews was badly judged when it really should have been reduced by at least £ 2,500. Standard STi should be £ 17,000 to compete closer to the Focus ST.