This week M&G, the biggest shareholder in Lonmin with a 17 per cent stake, openly rebuffed overtures from Xstrata, the Switzerland-based mining group, to buy its Lonmin shares, after the larger miner launched an unsolicited bid.

It was the latest sign of an institutional investor taking a robust stand amid a succession of bid situations, rescue capital-raisings and corporate governance rows – and the trend is set to accelerate as the economic downturn takes hold and fund managers fight harder to make their investment performance stand out.