1. A signal analyser for analysing and classifying an ongoing signal, the signal analyser comprising: a signal receiving device operable to receive a signal for analysis; a signal processing device in communication with said signal receiving device; a software application running on said signal processing device operable to process the received signal and identify the occurrence of any of a plurality of predetermined signal features, one or more belief index values, each distinct belief index value corresponding to one of a plurality of potential signal classifications, said software application including a classification engine operable to automatically increment or decrement said one or more distinct belief index values in response to the identification of predetermined signal features, after said belief index values are increased or decreased in response to identification of predetermined signal features, said belief index values being used to calculate belief index ratings, wherein each belief index rating has a magnitude, said magnitude relating to the likelihood of the corresponding classification being accurate, and by considering the relative belief index rating of each potential signal classification an indication as to the overall signal classification is obtained; and a notification unit in communication with said signal processing device, said notification unit being responsive to said classification engine for providing an indication of the classification of the signal based on the individual belief index; wherein said software application is operable to increment or decrement said belief index values according to an algorithm or a look up table of increments and/or decrements corresponding to the feature or features identified in the signal.