British outsourcing group G4S said its chief executive Nick Buckles would step down and be replaced by Ashley Almanza at the end of May after a string of setbacks at the firm which have hit its reputation.
G4S, the world's largest security group, warned earlier this month that its margin in 2013 would be lower than expected, sending its shares tumbling.
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Last year the firm saw its reputation hit after failing to provide sufficient security guard numbers for the London Olympics.
G4S said on Tuesday that Almanza, currently the firm's chief financial officer, was appointed following a process which considered both internal and external candidates.