The phone sitting on the table in front of Mark Campanale starts to buzz. Not recognising the number he excuses himself to take the call. Returning a couple of minutes later he catches the eye of his business partner, Pradeep Jethi: “Boris Johnson’s office. They want to talk about the Social Stock Exchange.”

The fact the Mayor of London's office is calling late on an unseasonally hot Friday afternoon to enquire about the Social Stock Exchange shows, if nothing else, that Campanale's and Jethi's vision for a dedicated marketplace for listing companies with explicit social or environmental aims is starting to get noticed.