Hi Darran, for deep cleaning conny roofs i would recommend a heavy duty degreaser based on micelles technology. dilute it 5-1 with water and pre spray the solution onto the surface, the secret to working with micelles technology is dwell time and agitation, because micelles technology is non-caustic, and non-corrosive, it will not break down the ingrained soils like high alkaline based chemicals do. but micelles solutions will not cause damage to UPVC,glass,rubbers,plastics,etc.
Again Darran if you google micelles technology you will find many suppliers in the UK.