Gartmore has admitted that Clive Roberts - an equities sales trader arrested last week on suspicion of insider trading - did a lot of business with the firm.
The admission comes after the fund manager suspended its star trader, a move that saw its shares take a tumble.
In a statement, Gartmore says: "Clive Roberts was a major counterparty of the firm when he was at ABN Amro but he has not been since he has worked for the Exane subsidiary of BNP."
A Gartmore spokesperson added that Roberts was a high profile client of Roger Guy, the firm's best-known fund manager. "But this in no way implicates Guy in insider trading in any way," she said.
Fears that Gartmore was becoming embroiled in the Financial Services Authority (FSA) probe into insider dealing, which led to seven arrests last week, first undermined the group's share price when talk centred on Roberts' relationship with Guy.
In its statement to shareholders, Gartmore says none of the "directed trades" - which are the subject of an internal probe into the dealings of the suspended Guillame Rambourg - were linked to Roberts.
The firm said that the investigation into Rambourg, which centred on unauthorised trades rather than insider dealing, was in its infancy and it said that termination of the Canadian's contract was "unlikely".
Rambourg has a 3.85% stake in the firm while Guy owns 5.56%.
Gartmore suspended star manager Rambourg following a week of intense City speculation that it could be involved in the massive insider trading investigation being carried out by the FSA.
Rambourg is now the focus of a major internal investigation after allegedly “directing shares”. The firm has said the incident is not related to the FSA’s highly publicised probe.
Gartmore fund managers must send their trades to a central desk for execution. It is understood Rambourg’s alleged breach involved trades made outside the usual central desk system although it is not known what, if any, advantage he is alleged to have gained.
Rambourg joined Gartmore in October 1995. He is a senior investment manager in the European equity team.
He and Roger Guy also co-manage the firm’s European hedge funds. Together Rambourg and Guy manage more than 20 per cent of Gartmore’s £21bn investments.
Major accounts include the Alphagen Tucana Fund, which rose 42% last year, and Alphagen Capella, which rose 12%. Gartmore said assets managed by Rambourg will be taken on by Guy.