Good question ModernDinosaur. From what I've read so far it's best practice to use Mode C when flying around Gatwick CTA and there is a strong chance of receiving at least a FIS if not a RIS from Gatwick according to Warped Factor.
If this is the case and given that there is a lot of GA traffic around the eastern end of Gatwick CTA I can see this veering towards a dramatic increase of GA aircraft asking for a service of some sort from Gatwick as it's long been a concern for pilots such as myself that there is no service offered around that area.
My gut feeling says that it would be great to be offered a "local" service in that area but given that Bewl Water is a major routing point, isn't this going to lead to Gatwick being overstretched?