A final day surge has meant almost 10,000 firms across the UK have posted their gender pay gap figures.

By 7pm, with just a few hours to go to the midnight deadline, the UK Government website recorded some 9,931 companies had submitted their figures as required by law. This exceeds the official expected estimate of 9,000.

It meant that more than 1,000 firms submitted their numbers in the last 24 hours. Such was the volume of traffic on the official portal that at one point on Wednesday morning it crashed.

Any company with 250 or more staff has had to file their figures or face the prospect of an unlimited fine.

The published data suggests 78 per cent of companies pay men more than women, 13 per cent pay women more than men while eight per cent have no gender pay gap based on the median measure.

Ahead of the deadline, Theresa May vowed to tackle the "burning injustice" of the gender pay gap.

The Prime Minister compared the pay gap to the women's suffrage movement a century ago, saying "major injustices still hold too many women back".

Her colleague Baroness Williams, the Home Office Minister, said she expected businesses to comply with the requirement to report their figures before the midnight deadline, noting: "It's a bit like tax returns; probably a lot of organisations will do it at the last minute."

Asked how companies could be pressed to publish a further document to show what they were planning to do to address their gender pay gap, Lady Williams said: "We are actually encouraging them to say what they will do…

“Some of the pressure will come from society but also from within those organisations themselves.

"Organisations actually want to do this. They really are trying to have a more gender equal workforce. I don't think we're actually pushing up against a closing door. This is something people want to see," she added.

Labour's Harriet Harman, a lifelong campaigner for women’s rights, said the pay transparency was "stripping away the veil and showing the pay discrimination".

The former party deputy leader noted: "What we've got is a pay structure which reflects how it used to be and not how it should be, which is that an hour of a woman's work is no less valuable than an hour of a man's work."

The London MP added: "What has to change is now we've got these figures published the management have to set targets for making progress year on year and they must be stretching targets, because nobody's interested in the justification, the excuses, the reasons anymore, actually it needs to change."

Hannah Bardell for the SNP said the publication of companies’ gender pay gap figures was “a start” but showed there was a “huge amount of work still to be done”.

The Livingston MP is one of a group of cross-party MPs supporting the #paymetoo campaign, set up to help ensure women don’t get “shut down” when asking about the gender pay gap at their workplace.

She noted: “In some cases the gender pay gap is enormous; rising to over 70 per cent. These figures are of course unacceptable and show the huge amount of work still to be done.”

Ms Bardell added: “Identifying the gender pay gap is a step forward. This must be translated into a real commitment by employers to get rid of this lingering injustice and ensure that every company and workplace has equality.

“It’s not just good for society; we know it is good for business and leads to better decision-making and higher profitability.’’