Next generation Wireless Sensor Networks will operate as self-regulated ad hoc networks of tiny devices that sense, actuate and communicate in a collaborative, autonomous and decentralised manner. This new context aligns with the paradigms of edge and fog computing where it is paramount to reliably distribute data among a large sub(set) of consumer/producer devices. This paper presents a communications architecture for scalable selective data dissemination in wireless sensor networks which is comprised of a decentralised data distribution layer that is tightly coupled to a reliable gradient-based routing protocol. The system supports mechanisms for selective data pushing and pulling within the sensornet where unstructured Peer-to-Peer content distribution concepts are utilised to fairly distribute pieces of data amongst an overlay of consumer and producer nodes. The system has been evaluated under a variety of network conditions and scenarios, both via simulation and real-world deployment, and it is shown to be reliable, scalable, and capable of distributing data in a fair and efficient manner across the network.