If I have the correct family, in 1851 Edward and Elizabeth, with children Martha and William were living in Oldfield Road, Salford. From GRO Index I deduce William's birth registered March Q 1851, Salford, mmn Parker.Edward Chester and Betsy Parker on same page March 1850, Warrington.Birth of Martha Parker (no mmn) registered Warrington March 1847.Suggest "P" for Parker.