In 1949, he won an Australian National University Scholarship to study for a PhD in neurophysiology at Cambridge. There he joined the laboratory of Drs. Alan Hodgkin, Andrew Huxley, Richard Keynes, and Peter Lewis who were developing new techniques in their pioneering studies of the physiology of single axons. While in Cambridge, Morrell worked with Silvio Weidmann in exploiting the use of microelectrodes to open a new chapter in heart electrophysiology by intracellular recording of ionic fluxes. At Cambridge he continued with his running and was awarded a Blue in athletics. In the 1951 Oxford/Cambridge Match all the events were equal – this meant that everything hinged on the relay. Morrell was the last Cambridge man to take the baton. There was an extremely good Oxford man as his opposite number but Morrell overtook him and thereby won the Trophy that year for Cambridge. In 1955, he graduated PhD.