We aim to perform zero and longitudinal field muon spin relaxation measurements in order to investigate anomalous spin dynamics effects observed in EuFe2(As1-xPx)2 with x=0.20 when ferromagnetism and superconductivity coexist at low temperature. In this system the Curie temperature is lower than the superconducting critical temperature, hence it offers an optimal playground to explore the interplay between the coexisting orders. The interplay between superconductivity and magnetism remains one of the main enigmas in Physics. The ISIS muon facility is the most suitable to measure slow muon spin relaxations of the longitudinal component expected for this compound and will be complementary to other techniques with different time windows, such as microwave and ac magnetization measurements.