Clifford joined Anglo American Corporation in 1986 and was seconded to E. Oppenheimer and Son as Harry Oppenheimer’s personal assistant in 1988. In 1990, he was appointed Managing Director of E. Oppenheimer and Son, a position he held until leaving in December 2004. During that time, Clifford was also a Director of Central Holdings, Anglo American and DB Investments. Following the privatisation of De Beers in 2000, Clifford served on the De Beers Executive Committee. Clifford formed Gem Diamonds in July 2005. Clifford is also the Non-executive Chairman of Zanaga Iron Ore Co. Limited.