Sir John Craven, the City veteran, is expected to announce on Thursday his retirement as chairman of Lonmin, the platinum mining group.

Sir John, 67, took over as chairman of sprawling Africa-focused conglomerate Lonrho in 1997 after the ousting of founder Tiny Rowland in 1996. He spearheaded the group’s move to focus on platinum mining, selling non-core assets and renaming the company Lonmin in 1999.