Her decision comes less than a year after chief executive Steve Corcoran quit the business following the discovery of a £5m black hole in the company’s overseas accounts.
Macpherson also unveiled results today which showed Speedy pre-tax profits slid by 38% to £7m after taking a £4.7m hit in the international business.
Revenue was slightly ahead at £350m driven by a batter second half, which saw hire deals struck with Babcock Group and Northern Gas Networks and Skanska.
Speedy has also been named preferred bidder for a Tier 1 contract with Balfour Beatty.
Macpherson said: “Without doubt, this has been a disappointing year of results for Speedy.
“The issues the group has faced in the Middle East have resulted in a financial impact, distraction in terms of management focus and general levels of disruption.
“These issues have now been addressed and we remain confident that the group has strong potential and the outlook is good.”
She added: “I believe that chief executive Mark Rogerson and his restructured and renewed senior management team are well placed to deliver on this and position the group well for the coming years.”