While I can fully understand things from Spar's point of view, as they were there first, the shop should accept that business is business and there will always be competition from rival businesses. Even just within Marple, there are examples of new newsagents, tanning salons, hairdressers, chip shops, cafes and even pet shops opening just a few doors away from similar businesses. When Marple Fish Bar opened a few years ago just metres away from Chius which had been there for years, I'm sure there was no talk of either business asking customers to boycott the other, constructing barricades, "keeping an eye on the competition" or all kinds of rumours circulating from various dubious sources. Also within the 2 years, two new newsagents have opened in the centre of Marple, I am sure other newsagents haven't resorted to such measures as those above. Likewise there are many pubs centred within a couple of minutes walk from each other in Marple, and I am sure the owners all accept there will always be competition.
Although having said that, I have never once used Marple Fish Bar but have always supported Chius simply because they were there many years before the competition.
Perhaps Spar and Premier could join forces and create one large convenience store, or maybe one could move to Marple Bridge which lacks any such store.