I lived for many years in near South Wimbledon and by the time I left, at one road there was a Tesco on one side, on the other side Sainsbury's and a Tesco petrol station a little way up the road!
Yes but I think that's different. It's called competition, and it's normal. But the Co-op seems to have decided to compete with itself! That could work if the new site generates completely new business or, as Andrew suggests, takes business from Iceland or Asda, although that seems unlikely, given that Asda and Iceland are cheap and the Co-op is not!
But if the new Co-op just takes existing customers from the Texaco site to the new one, then it doesn't make a lot of sense.
So it would not be a great surprise if in due course the Co-op were to relinquish the lease on the Texaco site, and it just becomes one of those generic garage-convenience stores, like the ones at Offerton and in Romiley.