The effects of a methane puff at three different plasma locations has been compared with a similar deuterium puff in a 2.5MA, 2.5T Elmy H-Mode. Changes in edge and core spectroscopic signals have been examined, and show that divertor methane sources are much better screened than wall sources. An intrinsic outer divertor methane source is derived, and shown to account for only about 15% of the carbon in the plasma core. Modelling with EDGE2D/DIVIMP, using 0.5 eV carbon atoms for the methane source, has been performed and compared with the experimental results.