An anonymous offshore investor has taken a 20% stake in the parent company of George Osborne’s Evening Standard, with the newspaper refusing to reveal the identity of its new financial backer.

The newspaper’s Russian owner, Evgeny Lebedev, sold about one-fifth of Lebedev Holdings, which has a majority stake in the Evening Standard, to a Cayman Islands-registered company in December, according to official filings that suggest the investor has put almost £14m into the lossmaking London newspaper.

The ultimate owner of the offshore company is unknown and Lebedev has refused to comment on suggestions made by the Financial Times, which first reported the news, that it could be a Saudi investor who has bought the shares, which come with the right to appoint two directors.

This has raised questions over whether an individual or company with links to the Middle Eastern kingdom could now have a significant financial interest in London’s main newspaper, which distributes 850,000 copies a day on the streets of the capital and is edited by a former chancellor.

A spokesperson for the company said: “Lebedev Holdings Ltd is a private holding company and as such we never comment publicly on our individual shareholders. We have no further comment to make in this matter.”

The links between Lebedev’s media businesses and Saudi Arabia have grown substantially over the past two years, despite concerns over the autocratic kingdom’s approach to journalists, especially after the murder of Jamal Khashoggi.

In 2017, Lebedev sold one-third of the Independent to a Cayman Islands company controlled by an obscure Saudi-based individual called Sultan Muhammad Abuljadayel. He stated on official forms that he was making the investment in a personal capacity, but he also works for NCB Capital, a division of a bank ultimately controlled by the Saudi government.

According to the FT, the recent anonymous investment in Lebedev Holdings was made by a Cayman Islands company founded by the same agent used during the Saudi investment in the Independent.

The Independent last week launched the first in a series of spin-off foreign-language websites funded, written and edited by a Saudi publishing company with close ties to the royal family.

This was despite concerns from some staff about the impact this could have on the neutrality of the main English-language website, whose editor, Christian Broughton, has previously flown to Riyadh to discuss the deal, although the Independent said it has appointed individuals to oversee the new site’s editorial output.

Last year, the Evening Standard ran an unusual and lengthy dispatch from the war in Yemen, in which the newspaper obtained substantial access to Saudi-backed militias.

The piece failed to mention Lebedev had accompanied the reporter on the trip, with many staff only finding out the newspaper’s proprietor had been involved in the story when he posted pictures on Instagram of him posing with soldiers.

Lebedev and his oligarch father, Alexander Lebedev, bought the Independent and the Evening Standard for £1 each a decade ago. The national newspaper has since gone online-only. The London-only newspaper briefly boomed under its free model, but has struggled financially in recent years due to the rising cost of newsprint and a declining print advertising market, recording a loss of £10m in 2017, which coincided with the shock appointment of Osborne as editor.

The anti-corruption organisation Global Witness has called on Lebedev to come clean about who is behind the substantial offshore investment.

“It is disturbing that people can secretly buy our newspapers and exert their influence from the shadows. Anonymous companies, like the one that now owns 20% of the Evening Standard’s parent company, should be a thing of the past,” said Ava Lee, a senior anti-corruption campaigner at the organisation.

“Last year, the government voted to end this secrecy in the UK’s overseas territories, including the Cayman Islands, where this company is registered. But these islands are dragging their feet. If the government is serious about ‘taking back control’, we must know who is really behind the curtain.”

The paperwork relating to the outside investment in Lebedev Holdings was filed on 27 December, shortly after the resignation of the long-serving Lebedev employee Justin Byam Shaw from the holding company’s board.

Lebedev, 38, has a luxurious lifestyle, regularly flying celebrities out to his Italian villa and attending London theatre events. He also turns his hand to journalism, where he is fond of writing pieces on the need to save elephants.

Last year, Lebedev was appointed creative director of the Evening Standard magazine’s theatre awards photoshoot, taking the decision to place himself in the photos alongside the actors Claire Foy and Idris Elba and Vogue’s editor, Anna Wintour.