The location of the supermarket in Hibbert Lane contravenes Council planning policy. If my recall is accurate,this was also stated by the MP in the 'Gridlock' leaflet that you refer to. In addition to which I believe that comment was made by only one Councillor (SA) and she will simply say that the Marple Supermarket issue has changed out of all recognition, since she made that comment - which of course it has.
SMBC planning policy allows for the siting of a retail development in town centre. Trinity Street qualifies as being in the town centre ASDA DOES NOT. Our Local Councillors are SMBC Councillors. So naturally we would expect them to support Council policy - wouldn't we? Surely we elected them to represent us to the Council and the Council to us. So where is the argument? If there has to be supermarket in Marple and it seems that there has to be then surely the Council (this includes our Councillors as they are on it) will support its own policy. To suggest that there is some way that they will do something else is surely a futile argument.
Whilst this continues to be a two horse race between ASDA and Kirkland then the actual decision will come outside the Council and it will depend on whether ASDA choose to appeal and whether Kirkland can successfully relocate the sorting office and resolve the not unimportant issue of finding a client, neither of which they have yet managed to do. Both ASDA and Kirkland have a strong influence on each other.
The issue is nothing to do with traffic. There will be increased whatsoever the choice. Traffic will probably be worse at Trinity Street than at Hibbert Lane as all the Supermarket traffic from the High Lane/A6 will stop at Hibbert Lane and not come into Marple whereas the Trinity Street scheme will bring all the traffic into Marple Centre. Plus the ASDA car park has more spaces than Kirkland's and is therefore less likely to overflow. However, traffic implications will not stop these schemes nor will local Councillors nor will SMBC. These schemes will only be stopped by each other. Only ASDA can stop Kirkland and only Kirkland can stop ASDA.
Currently, they are waiting for each others' next move but these moves will come be after the local planning decisions have been made, early next year. Whosoever leves town first is the loser. Arguments about traffic, although traffic it is a real issue, are just red herrings and will not stop either of these schemes.