In good times, investors in News Corp fret about “the Murdoch discount” – the worry hanging over the stock that at any moment its dominating chairman and chief executive might decide to spend shareholders’ money on a large investment with uncertain payback.

When markets go into reverse, as they have been for some time, the cost of such sprees come under sharper scrutiny. On Thursday, Rupert Murdoch announced an $8.4bn non-cash impairment charge against the group’s assets, including a 50 per cent cut in the value of Dow Jones, the publisher of the Wall Street Journal for which he splashed out $5.7bn in 2007.