The shares in Gartmore have fallen more than 10 per cent over the past week amid speculation about links between Roger Guy, a Gartmore fund manager and Clive Roberts, head of equities at Exane BNP Paribas.

Gartmore categorically denies any wrongdoing by staff. "No one from Gartmore is involved in the investigation," a spokesman for Gartmore said.

Mr Guy manages more than 20 per cent of Gartmore's £21bn investments, alongside Guillaume Rambourg, his co-manager. The pair account for about 40 per cent of group revenues, including performance fees.

Seven men were arrested last week as part of the FSA investigation into insider trading. Leading City banks BNP Paribas and Deutsche Bank, as well as US hedge fund Moore Capital and boutique London broker Novum Securities, have all been drawn into the investigation.