Toscafund, the £3.5bn ($6.9bn) London hedge fund, has overtaken Lansdowne, a rival hedge fund group, as Aberdeen Asset Management’s biggest investor.

The two hedge funds now own more than a quarter of Aberdeen’s shares after Tosca – led by former banking analyst Martin Hughes, who backed Virgin’s bid for Northern Rock – increased its stake to 15 per cent. Lansdowne has long held 11 per cent of Aberdeen.

Tosca first emerged as a big shareholder in Aberdeen last month when it bought close to 10 per cent of the group after its shares sank to a two-and-a-half year low of 117¾p.

Aberdeen’s shares fell 2.4 per cent on Monday to 131¾p after an earnings downgrade by Numis, the broker.

Numis said it was cutting its forecast for Aberdeen’s earnings in 2008 and 2009 by about 13 per cent to 11.3p and 13.6p respectively as a result of the deteriorating fund inflows.

“In light of continued equity market weakness we reduce our assumptions for investment performance and net fund flows in the fixed income business which lowers our earnings estimates,” analysts at Numis said.

This was the latest in a string of downgrades in the sector as analysts have factored declining markets and an economic downturn into estimates. Henderson last month warned that falling investor confidence in markets would have a direct impact on fees and revenues.

Evolution Securities has downgraded its earnings expectations for Aberdeen. Its analyst Jason Streets said: “Aberdeen’s asset mix [heavy fixed income weighting] makes it more defensive than some but not invulnerable to equity market downward lurches.”

Evolution cut its estimates for Aberdeen’s assets under management by March from £102bn to £99bn, which would hit revenues from Aberdeen’s higher margin equity funds. Neither Numis nor Evolution turned sellers of the stock.

Aberdeen has fared better than many other asset managers during the market turmoil.

Funds under management rose 8 per cent in the final quarter of 2007 in spite of a rise in asset outflows. Many managers suffered net outflows in the same period.