Guillaume Rambourg, one of the star hedge fund managers at Gartmore, has quit the company as an investigation by the Financial Services Authority into breaches of internal trading rules rumbles on.

After a brief suspension in March from his role of portfolio manager along side Roger Guy, Rambourg was reinstated in April as an analyst pending the outcome of an internal investigation by solicitors Clifford Chance into possible breaches of Gartmore’s trading procedures. That investigation found no suggestion of dishonesty in his conduct, though a separate probe by the FSA, triggered by the suspension, continues.

Announcing his resignation Wednesday evening, Rambourg said: “I have taken the very difficult and personal decision to resign from Gartmore after more than 14 years so that I can devote all of my attention to co-operating with the FSA’s investigation and regain approved status.”

“I have been faced with a challenging set of circumstances which has resulted in me not being able to optimally fulfil my duties in the best interests of shareholders and investors. I have, therefore, concluded that in the short term at least it is in nobody’s interests to continue in my current reduced capacity.”

Guy and Rambourg ran the biggest portion of Gartmore’s equities fund management business being responsible for around one-third of total revenue when the firm floated in late 2009. However, the dependence on the pair was lessened in January with the recruitment of John Bennett from GAM to run several long-only funds as well as a new equity long/short fund.

Gartmore continues to appeal a €300,000 fine levied against Rambourg by the Italian markets regulator for abusing privileged information in 2006. The US Securities and Exchange Commission is also probing an alleged US trading rule breach last year.

Shares in Gartmore fell 7% early Thursday to 102 pence. It floated at 220p in late 2009 on the London Stock Exchange with Rambourg and Guy among the leading shareholders.