The European Commission’s own monitoring of compliance has shown that there was a lack of compliance across many EU states, many of whom were failing to implement national legislation to implement the EU directive on equal pay. The Commission concluded that, overall, member states had not used the opportunity to review their national systems in a comprehensive way or to simplify and modernise their equal treatment legislation.

A research paper prepared in advance of the plenary session says that sex discrimination in the labour market and workplace, and failure to ensure equal opportunities for women and men in employment have significant costs for individuals, and for European societies and economies more broadly.

The report states that on average, women in the EU currently earn around 16% less than men, which results in an even wider gender pension gap (39%). It says that a European-level initiative to revise the current directive on equal pay for both sexes could boost EU GDP by around €13bn (£9.6bn) per year.

The European Women's Lobby (EWL) has stressed that the Directive has failed to close the gender pay gap, and is calling for more stringent measures, including legally binding provisions, such as mandatory pay audits to strengthen wage transparency.

A separate report from Grant Thornton International, Women in business: the value of diversity, scrutinises the financial performance of companies listed on the FTSE 350, CNX 500 and S&P 500. The analysis shows that increased diversity of perspectives on executive boards leads to them outperforming their all-male run peers.

The study, which covered listed companies in the UK, India and US, put the opportunity cost for companies with male-only executive boards (in terms of lower returns on assets) at £430bn in 2014.

In the US, S&P 500 companies with diverse boards outperformed rivals by 1.91%. In the UK FTSE 350 the gap was 0.53% and for the Indian CNX 200, 0.85%. This translates into an opportunity cost of around £372.5bn, £48.5bn and £9bn in each of the three markets respectively - or around 3% of GDP in the UK and US.

Sacha Romanovitch, CEO of Grant Thornton UK, said: ‘So we have the evidence that businesses with more diverse teams give better business performance. These progressive firms are delivering a competitive advantage for their stakeholders, finding it easier to attract talent and building better business relationships. It matters that we get this right – and more and more we are seeing that it requires intentional action by leadership teams to effect a change.’

The EU report, Towards gender equality in employment, is available here

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