1. A routing method for an ad hoc network, the network comprising two or more nodes, the method comprising sending a message from a start node to a finish node via one or more intermediate nodes forming an ad hoc path of communication through the network; the start node receiving an acknowledgement signal from a one-hop neighbouring node when the one-hop neighbouring node receives the message from the start node, and the start node receiving an acknowledgement signal from a two-hop neighbouring node when the two-hop neighbouring node receives the message from said one-hop neighbouring node; the or each intermediate node in the path of communication, in turn, receiving an acknowledgement signal from a respective one-hop neighbouring node downstream of it in said path when the respective one-hop neighbouring node receives the message from the respective intermediate node upstream in said path and, except in the case of the one-hop neighbouring node being the finish node, each intermediate node receiving an acknowledgement signal from a respective two-hop neighbouring node, which is downstream of it in said path, when the two-hop neighbouring node receives the message from the one-hop neighbouring node which is upstream of said two-hop neighbouring node in said path.