According to statistics published by the financial firm, almost Â£1.7 billion was withdrawn by clients in the six months to June 30th.
A further Â£238 million was taken out of the company during July.
Guillaume Rambourg, a hedge fund manager at Gartmore, was suspended by the firm and later resigned earlier in the year after the Financial Services Authority announced an investigation into irregularities surrounding access to direct trades.
Jeffrey Meyer, chief executive officer at Gartmore, said: âOur net sales were below expectations primarily due to the suspension and subsequent resignation of one of our portfolio managers.
âWe are now focused on regaining momentum and believe we are attractively positioned to benefit from the continuing demand for absolute return products and the general growth potential of our UK retail business."
Further findings from the firm showed that net revenue increased by 36 per cent to Â£113.2 million during the first half of 2010 when compared to the same period last year.
By Jim Ottewill