Paul Mercer was resident in Durban from January to August 1979, when he was
transferred back to Johannesburg. I believe that he worked as a civil engineer.
During his short stay he won the First Swiss with 8/9 (8 wins, loss to Rust) and then
the Durban championship with 6½/9 (4 wins, 5 draws). Paul showed a predeliction
for unusual openings, which unsettled several strong opponents. His game against
Gerald Boulle is given below.
Paul was rated just under 2200 during 1979, which placed him in the top 10 of the South African rating list. However, I don't think he ever participated in the SA Closed championship. He left South Africa around 1995 and returned to England, where he was a member of the Ashtead Chess Club (not far from London).
Here is a game from the First Swiss, where Paul outplays his opponent in the middle game: