OK, so I admit it, I am a bit biased with this story as Metrica works with both Green & Black's and Phipps PR but I still thought it well worth a mention here. 

Carol Welch, Green & Black's Marketing Director claims that PR has been the biggest reason behind the brand's success 

Commenting on Real Business' blog, Carol says: 

“Some people think PR is just spin, but it is certainly as important as advertising or any other part of the overall marketing of the business.  It is a mistake to think otherwise."  The big difference, she says, is that PR generates word-of-mouth marketing, something much more effective than straight advertising.  “We use a firm called Metrica to track the coverage we get. It works out how much the coverage is worth financially and whether or not we are getting the messages across, which, in the case of Green & Black’s, is the ethical sourcing of cocas beans.”

As the article concludes :

"One thing is for certain: it works. In five years, the Green & Black’s brand has gone from being worth £5m to today being worth £40m."

So there you have it, the proof it would appear is in the pudding.  Mint choc chip ice cream anyone?