After reading archaeology and anthropology at the University of Cambridge, he became a lecturer at the University of Bristol in 1963. Fascinated by the Roman remains in nearby Bath he threw himself into a programme of excavation and publication. His energy and intelligence drew attention and in 1966 he became an unusually young Professor of Archaeology at the University of Southampton. There he became involved in the excavation (1961-8) of the Roman palace at Fishbourne, Sussex.
Another southern site led him away from the Roman period. He began a long series of summer excavations (1969-1988) of the Iron-Age hill fort at Danebury in Hampshire. He continued to work at Danebury after moving to Oxford in 1972 and is currently involved in the Danebury Environs Project. His interest in Iron Age Britain and Europe generated a number of publications and he became an acknowledged authority on the Celts.
He was President of the Council for British Archaeology 1976-79. He has been a member of the Ancient Monuments Advisory Committee of English Heritage since 1984 and of the Advisory Committee of the Discovery Programme (Ireland) since 1991. He is a Governor of the Museum of London.