They have hinted at it being a 'high quality' retailer. This would certainly appease many of MIA who are vocal about Tesco/Asda being evil capitalist giants they do not want in Marple. I would guess it is a Waitrose. However this still leaves a gap in Marple for those on low incomes that need the convenience of a supermarket. To them it will seem that MIA/snobbery/hypocrisy has taken place.
I also have a feeling that IF Asda is turned down at appeal and Trinity goes ahead, MIA may then decide to protest. Especially if it turns out it would be Tesco/Asda/Aldi/Lidl. They can't seem to make their minds up and many arguments they put forward against HL also apply to TS eg. traffic choas, driving local shops out etc.