I agree Moorendman, a tesco (or any other large supermarket) will undoubtedly impact on local traders, and on the traffic.
In my humble opinion, Marple is getting too big, and has lost the "village" feel that it had when I moved here 22 years ago. One of the lovely and unique things about Marple is the variety of small local shops, and although I do the bulk of my shopping in Sainsburys, I visit the local butchers, fishman and greengrocers weekly, as well as the deli for special cheeses, gifts etc. The quality of meat and fresh veg is a million times better than from supermarkets.
And I use the co-op for extras at least weekly, ok so it's not huge, but it stocks the basics and I have never found the staff to be any worse than in any supermarket.
Just my opinion though