Former employees of the Co-operative Group have launched legal action against the employer over unpaid bonuses worth around £1 million.

The 10 employees, who worked for Co-operative Insurance Society, the mutual’s insurance organisation, which was sold to Royal London in July 2013, have launched formal grievance proceedings against the Group.

The move follows the employer’s decision, in February 2013, to change its bonus structure for employees in its banking arm, to focus on customer service rather than sales targets.

In March 2013, the Co-operative Group posted a pre-tax loss of £662 million, down from a £138 million profit in 2012.

The employees, who worked as fund managers, have argued that they were not responsible for the losses and should subsequently be rewarded for their work.

The Co-operative Group confirmed that the proceedings are underway, but declined to comment on the dispute.