Are house prices pushed up by upmarket supermarkets?

The BBC tweeted out this story discussing what is now being referred to as The Waitrose Effect.

The Waitrose snobbery/property price index https://t.co/utNDOkANO3

— BBC News (UK) (@BBCNews) October 26, 2013

Waitrose, an upmarket chain of supermarkets in Britain, has property owners in Helensburgh, near Glasgow, attributing their property price rises to the opening of the new store.

In a story entitled The Waitrose snobbery/property price index, the UK BBC reporter Kathryn Westcott notes the following: "The effect has been studied, by estate agents at least. Savills's research indicated that house prices in areas where there was a store were typically 25% higher than the UK average. In London, there was a 50% premium in Waitrose postcodes."

And then she asks the million pound question.

"But like the chicken and the egg, is it a case of Waitrose following affluent customers, or does the opening of a branch make an area more desirable?"

Do you think that the opening of upmarket stores in an area helps increase property prices? Or is it, as Westcott suggests, a result of affluent customers growing in an area?