A simple principle lies at the heart of pension investment: the pension manager must invest in the best interest of the client. UK ministers have often wished UK funds would show more home bias by channelling more pensioners’ cash towards domestic assets in the interests of economic growth, but the fundamental rule of the game has always been understood. You don’t mess with the fiduciary duty. Thus, when Rachel Reeves a year ago unveiled her Mansion House accord – a pledge by 17 of the biggest providers to earmark a slice of workplace pensions for UK private assets – it was made clear the arrangement was voluntary. What’s more, as the signatories emphasised, the commitment was “subject to fiduciary duty and the consumer duty” and “dependent on implementation by the government and regulators of critical enablers”. Those essential qualifications, one could say, weakened the force of the accord, but what else could the chancellor do?…