Cabinet ministers must demand sectors under their remit produce action plans to reduce their gender pay gaps, reporting back within six months, Theresa May has said.

The gender pay gap has fallen slightly from 19.8% in 2010 to 18.4% in 2017 but on current projections will not close for another 34 years, the cabinet was told.

Penny Mordaunt, the international development secretary who had taken on the women and equalities brief just 24 hours earlier following the resignation of Amber Rudd, said ministers should ask key sectors covered by their departments what they were doing to close the gap.

Mordaunt said she would report back to the cabinet by November, with ministers expected to feed in from their departments.

Speaking to the cabinet, May said the UK should be proud to be one of the first countries in the world to introduce gender pay gap reporting in over 10,000 large companies. All public sector bodies have now reported, Downing Street said, with 97% meeting the deadline.

However, the government is understood to have contacted 1,500 companies to demand an explanation as to why they have not complied.

“The PM said this has significantly raised the exposure of the issue across the country and is an important first step in driving the cultural change that we need,” May’s spokesman said, pointing to the culture shift that the reporting had already precipitated in key employers, such as the BBC.

The figures released over the course of the past few months showed eight out of 10 employers pay men more than women. The Equalities and Human Rights Commission is responsible for enforcing the law for companies with over 250 employees to report their pay figures.

However, MPs have recently questioned its capacity to enforce the law given the cuts to the EHRC’s funding.

The construction sector, which will fall under the new housing, communities and local government secretary James Brokenshire’s brief, reported the worst average median gender pay gap at 25%. This was followed by finance and insurance at 22%.