RAB Capital’s flagship hedge fund has plunged by almost half this year after it wrote down stakes in private companies including A1 Grand Prix, the motor racing series, and will be shut unless investors agree to lock up their money for three years.

RAB, one of a handful of London-listed hedge fund managers, yesterday confirmed a report in the Financial Times that it was asking investors in RAB Special Situations not to withdraw money, in return for a cut in fees. It said if it did not receive 75 per cent support the only “equitable” option would be to wind up the $923m fund.