I am 100% sure that it is not a coincidence that plans for the supermarket have not as yet been submitted...... But times have changed and we must remind our elected members that they are to be more accountable now than ever.
You are correct, but please don't sniff out conspiracy again. This is absolutely standard practice for developments of a resaonable size. What developer would want his scheme to be used as a local political football? Despite planning having nothing to do with politics, it doesn't stop local Councillors trying to get elected off the back of tub-thumping, when in reality they have little influence in the long run. And neither does it stop pressure groups trying to bully Councillors in the same manner.
Your second point that I have highlighted above is an interesting one. Short of a referendum how do we actually know what the majority of Marple want? Is it a case of whoever shouts the loudest must be right? Again, politics has no part in planning decisions, other than to get them wrong (which then gets corrected at public inquiry at tax-payers expense).
If, for the sake of argument, MIA were to field a candidate and win then I'm not entirely sure what good it would do in the long run - given that the Council are going to refuse any retail application at Hibbert Lane anyway on policy grounds, and there is no way that any MIA Councillor would be allowed onto the local planning committe to vote on such a subject, due to their stated bias. After this initial Council decision any Councillor wouild have little or no influence on any later planning appeal stages anyway. I suspect this is why MIA haven't gone down such a route.