And former group finance director David Lindsay has announced his intention to leave with immediate effect.
That comes three months after Lindsay became operations director on handing the finance director role to Mark Adams in April.
The announcement came the same day as the group announced its intention to raise £45 million through a placing of 40.8 million shares at 110p per share with institutional investors, an 8.9% premium over the previous day's mid-market 101p share price.
Helphire said Jackson will remain with the company until a successor is appointed and handover is completed.
A recruitment process has already begun.