The fund, chaired by Sir George Mathewson, bought a 9.8% stake in Aberdeen in March 2008 when the shares had dipped below 120p, and by June had increased the stake to above 25%, buying at prices above 130p. Toscafund said the investment was a “strategic” stake.

All but 4.99% of the shares have been sold, most of them in recent weeks, with Aberdeen’s shares above 140p.

But the sale has been forced by a restructuring of Toscafund, with founder Martin Hughes in the process of liquidating a portion of the fund to meet calls from investors.

Toscafund began the year with Aberdeen as its biggest investment, at a time when investors were pressing to withdraw cash and putting the hedge fund under pressure after it lost 50% in 2008.

At the time Toscafund reassured investors that Aberdeen offered “100% upside” for those holding on for a year, as well as a 5% dividend. Aberdeen shares were down 2.2p at 145.7p yesterday, a rise of 16% since the beginning of 2009. Toscafund was up 40.3% in the first eight months of the year.

The fund halved its stake from 18% to 9% last week and has sold another 4% this week. Of 20 analysts logged by Bloomberg, 14 currently have buy or hold recommendations on the stock.

Aberdeen shares sank to 80p last November, but bounced back at the end of the year when it announced the deal to buy much of Credit Suisse’s asset management business.

The Swiss bank became Aberdeen’s dominant shareholder with 24%, arriving hard on the heels of Mitsubishi, the financial giant once seen as a bidder for Aberdeen, which took a 9.9% holding a year ago as part of a Japanese distribution deal.

Last month Mitsubishi crossed the 15% threshold at which it was entitled to nominate a board member, which it has done. It now appears to have picked up some of Toscafund’s stake, taking it to the 19.9% limit which it has promised to observe until at least next year.

Toscafund was the catalyst in 2007 for the auction of ABN Amro and its acquisition by RBS, the bank formerly chaired by Mathewson.

The Herald reported earlier this year that the ill-fated RBS deal helped Toscafund’s limited liability partnership make a profit of £158m on turnover of £181m in 2007.