Are you/ Have you been a member of the Audience Research Board for official television ratings?

We just received a postcard from the Audience Research Board asking us to become a member so they can measure our viewing activities for the official UK television ratings, apparently only a few thousand homes across the country are selected for the survey. There is apparently an incentive scheme whereby you earn points to exchange for items on a website, however I cant find anywhere how you go about earning the points, how many points you get, when you get them etc, does anybody else have any experience of this who could guide me?