His excavations included the Great Witcombe Roman Villa, Gloucestershire (1960–1973), and Chew Valley Lake, north Somerset (1953).
Greenfield grew up in Sidcup, Kent and was a schoolboy when he set out single-handedly to excavate a Roman site at Horwood's Pit, St. Pauls Cray, whilst gravel extraction operations were being carried out in the 1930s.
Hogg later drew up a plan of the site, and sought further help for Greenfield from Norman Cook at Maidstone Museum.
In a letter to Cook, preserved at the museum, Hogg stated that Greenfield 'had the right ideas, but was discouraged 'after having lost his finds and site notes off the back of his motorbike!'
Later Greenfield set up a local archaeological group which discovered many new sites including the famous Lullingstone Villa.