Half of companies who have filed figures so far have managed to narrow their gender pay gap in the first year of reporting, a Guardian analysis has found.

Since 2017, it has been compulsory for companies with more than 250 employees to report their gender pay gap figures by the end of every financial year. The first round of data, submitted by the deadline last year, showed men were paid more than women in 7,795 out of 10,016 companies and public bodies in Britain, based on the median hourly pay. Only one in five companies expected to report have filed figures for this year.

Of the 1,510 companies who have reported to date for both years, 756 (50%) improved their gender pay gap. A further 5% (72 companies) made no progress on closing the gap, 39% (592 companies) reported a worse gap than last year, and 6% (90 companies) reported a 0% gap for both years. The most recent figures refer to the 2017/2018 financial year, while the previous year’s data covers 2016/2017.

Among the companies to have reported the biggest improvements so far is Monzo, the digital bank. Its pay gap improved by 34%, from 48% last year – meaning women earned 52p for every pound men earned – to 14% this year. This compares with 17.9%, the average median pay gap for both full and part-time workers, according to the ONS.

However, its top quartile of earners was still heavily male-dominated. The company reported just 20% of its highest paid employees were women.

Tara Mansfield, the head of people at Monzo, said that among the reasons for the change was that the team had more than trebled in the past year, some women had been recruited to senior positions and others had been promoted internally.

“We have committed to making roles at Monzo as attractive as possible to all kinds of people so we can have a representative workforce,” she said. “Some of the initiatives we’ve launched have been flexible working, a generous caregiver scheme and mentorship opportunities.”

Svitzer Marine Ltd, a ship towage company, reported a 30% improvement in its gender pay gap, from 45% last year to 15% this year. Kasper Friis Nilaus, the managing director of Svitzer Europe, said the maritime industry was traditionally dominated by men, but that the company’s improved pay equality figures reflected the promotion of “more talented women” to management jobs. While the gap has narrowed, the company’s workforce is predominantly male and 96% of Svitzer’s top quartile of earners are men.

Montsaye Community Learning Partnership, an academy trust in Northamptonshire, also reported a large improvement, from 51% to 21%. They said that, while they would like to take credit for the improvement, the main reason was the significant increase in pay for local government employees – 9% in some cases – set by the Local Government Association.

“As we are a group of schools, our gender balance is heavily weighted towards female staff, the majority of which are part-time. This high pay rise in the lowest grades predominantly occupied by female employees therefore narrowed the gap without any proactive action from the trust,” they said.

Banks have reported some of the worst gaps in the figures so far. Credit Suisse International reported a median gap of 45%, while Credit Suisse UK reported a gap of 29%. Barclays Bank plc reported a median gap of 44%.

Multi-academy trusts also account for a significant proportion of the highest gaps so far. Nexus Education Schools Trust, a MAT made up of 10 schools in south London, reported a median gap of 58%.

Charles Cotton of the Chartered Institute of Personnel and Development said it was too early to draw conclusions from the gender pay gap figures that had been reported so far. He said there were few quick fixes for closing the gap.

“You’ve got to look at what’s driving the difference,” he said. “Some gaps can be closed by employer action, such as, for instance, flexible working arrangements, for those who have care commitments.

“But some of the gaps can’t be closed so easily because of things that happen outside the workplace, like the availability of low-cost, high-quality childcare or elderly care, or societal assumptions about who should be looking after the children or the elderly.”

Hephzi Pemberton, CEO of the Equality Group, said that one of the most effective ways to close the gap was to get women into the highest paid positions. “That’s where the chasm really occurs,” she said.

“There are quite a lot of statements around about junior and graduate intakes at various organisations and that’s very good, but it’s not going to move the numbers as quickly as getting more women into senior and more economically powerful positions.”

She said she expected this year’s gender pay figures to see a marginal improvement. “I think there’s a huge amount of work for a lot of organisations to do and it isn’t work that happens within a year,” said Pemberton. “It’s cultural change, but also just practical ability to change the make up of senior executive leadership and that can take whole careers to shift.”