When the two Canadians at the top of BHP sit down in a couple of months time to decide whether to spend $US5.7 billion ($7.4 billion) on a new Canadian potash mine, they will do so knowing the loudest critic of their plans will likely be silent.

Charles “Chuck” Magro has been a constant irritation for BHP in recent years as his regular warnings that BHP’s Jansen mine in Canada would flood the market with too much potash have frustrated attempts to convince BHP investors of the merit in taking a long-term punt on the fertiliser commodity.