RM CEO Terry Sweeney has handed in his resignation in the wake of an operational review completed at the end of September.
In an early morning statement to the City, RM said Sweeney had decided the time was right "to pursue his career outside RM" and said the split came "by mutual agreement".
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Rob Sirs, who had previously decided to leave the firm after 21 years of service, has been reappointed to the board as group managing director, with responsibility for RM's operating businesses.
Meanwhile the firm has also appointed non-executive chairman Martyn Ratcliffe, who signed on in June to oversee RM's operational and strategic review, as executive chairman.