Hmm. I wouldn't bank on that. No doubt the Co-op will keep the Texaco garage site open for a while after the new branch has opened, but if the takings go down at Texaco (which they probably will), then I should imagine they will give it up.
I used to near a Tesco Express Petrol Express in South West London. Tesco bought a pub 100m away, closed it down and opened another Tesco Express in the pub building.
Both Tesco Expresses remain open to this day.
I'm pretty sure Co-op wouldn't be taking on another store if they didn't think they can make having two work. Given the position of the new store, I suspect it's likely to be Asda and Iceland that stand to lose from it. But equally it could bring in more customers due to the sheer convenience of having a late opening store on their doorstep.