A partial sell-down by one of Platinum Asset Management’s biggest backers follows a steady decline in the company’s stock price towards an all-time low, and a pot of client money that has largely failed to grow in the five years ruled by a radically different style of investing.

Billionaire arts and journalism patron Judith Neilson, the former wife of Platinum founder Kerr Neilson, sold 97.3 million shares equal to 16.6 per cent of the company on Thursday at a 6.5 per cent discount to their face value in one of the biggest block trades of the year.