Global brewer SABMiller
The move appears to fly in the face of the UK corporate governance code which suggests that chief executives should not go on to become chairman of the same group, although the code does say this can be allowed if the company consults its shareholders and sets out clearly the reasons for its decision.
The 52-year old South African Clark will be appointed chief operating officer at the group's annual general meeting this July and work closely with Mackay who becomes executive chairman for a year until becoming non-executive chairman from July 2013.
SABMiller argues the group has gained from its stable team of current Chairman Meyer Kahn and CEO Mackay since the group listed in London in 1999, and Mackay has great experience of the worldwide brewing industry and especially emerging markets.
The world's second biggest brewer and maker of Miller Lite, Castle and Peroni beers has written to shareholders outlining its reasons, pointing out that Mackay has spent 34 years with the group and is highly regarded by industry and stakeholders.
Clark joined the brewer in 1990 and worked in South Africa before becoming managing director of SABMiller's European operations in 2003 where its main markets Poland, the Czech Republic and Hungary showed strong growth in his early years but, latterly, declining volumes as economic conditions worsened.
In other moves, Kahn retires as chairman at the annual general meeting this July, and Sue Clark, the group's director of corporate affairs, will take over from Alan Clark as head of European operations.
In 2008, Marks and Spencer's
Rose came under pressure from shareholders for his dual role which was against the recommendations of the governance code and stepped down from the CEO role in May 2010 and then as chairman in January 2011.
(Reporting by Adveith Nair and David Jones; Editing by Paul Hoskins)