(Bloomberg) -- More than half a million female managers will have to be added in the UK before supervisors reflect the labor force, according to a report by the Chartered Management Institute that highlights a failure by companies to develop female talent.

The data adds to a wealth of evidence of female underrepresentation in the best-paid roles in UK business. Half of the country’s smaller listed companies still have all-male leadership teams, while Aviva Plc Chief Executive Officer Amanda Blanc said that the sexism she encounters has worsened as she has risen through the ranks in finance.

The shortfall of women managers, which the CMI says is set to worsen in the coming years, has already prompted action by regulators. Earlier this year, the Financial Conduct Authority set listed companies a goal of at least one woman in the role of chief executive officer, chief financial officer or senior independent director.

To address the significant shortfall of managers from underrepresented groups, including women, the report calls on the government to commit to wider pay gap reporting and avoid awarding contracts to companies that consistently fail to diversify their leadership teams.

The report also found significant underrepresentation from other groups among managers, including:

  • 420,000 from lower socioeconomic groups
  • 100,000 from diverse ethnic groups
  • 290,000 from disabled backgrounds

Leaders should embrace flexible working and make boosting diversity a central part of all managers’ roles as part of their efforts to improve representation, the report suggests. 

Employers and the government need “to step up and accelerate the pace of change especially as growth is faltering and thousands of employers see skills shortages,” Ann Francke, chief executive officer at the CMI, said in the report, published Thursday.

The CMI also found a discrepancy between how companies perceive themselves and how they act. For example, 83% of firms said they were inclusive of people regardless of their class but just 26% were taking active steps to increase the proportion of employees from lower socio-economic backgrounds. 

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