I've seen a discussion on here about an alternative site for a supermarket but can't find it again.
The suggestion was that the area of the car park behind Market Street and the sorting office building (assuming that RM was in agreement) would be a suitable place. In fact there is scope for enlarging this area.
The buildings on Market Street, built in 1805, between the Pineapple and the Bulls Head (not sure if the Bulls Head was included) have had a "slum clearance" order on them since before the war and as far as I am aware this has never been rescinded. It certainly hadn't in 1983 when my father retired and sold the shop premises as there was a minor kerfuffle about it in the conveyancing. As a child we lived "over the shop" on this part of the street and I remember being appalled that a row of shops and (at that time) houses which was built in the year of the Battle of Trafalgar should be marked for demolition! (I think I still would but that's another story!)