The chief financial officer of scandal-hit mining company Ferrexpo sold shares worth more than £400,000 the day before the FTSE 250 mining company lost almost a third of its market value.

Chris Mawe sold 150,000 shares worth a total of £402,045 on Thursday, hours before accounting firm Deloitte resigned as auditor following a scandal surrounding potential misappropriation of money paid by Ferrexpo to a charity called Blooming Land, which supports local social and health projects in Ukraine.

Deloitte’s resignation triggered a 28% fall in Ferrexpo’s share price on Friday. At the time of writing Ferrexpo’s share price was £2.07, about 23% below the £2.6803 price at which Mawe sold.

In a statement to the stock market, Ferrexpo said Mawe had sold the shares “to settle tax and social security liabilities” which arose when he received the shares under his long-term incentive plan after the company’s 2018 annual results. Mawe joined the board of the company, which mines iron ore in Ukraine, in 2008.

Ferrexpo said: “At the time of the decision and execution of the share sale, neither Mr Mawe nor the company had received Deloitte’s letter of resignation.”

However, in a separate statement published by Ferrexpo on Monday, Deloitte said it had threatened to resign in January after Ferrexpo delayed an investigation into discrepancies in the charity’s bank statements.

Deloitte, one of the big four accountants, warned Ferrexpo in October and again in November that it expected an independent forensic review into the discrepancies if Blooming Land did not provide the requested evidence.

Ferrexpo, which is headquartered in Switzerland, appeared to agree that an investigation was necessary, Deloitte said, but the board voted in January not to start an inquiry. Instead, Ferrexpo wrote a letter to Blooming Land requesting further clarification.

Ferrexpo only agreed to carry out a review after Deloitte’s threat to resign in January. The law firm Herbert Smith Freehills and BDO, another accounting firm, have been appointed to carry out the review, alongside Ukrainian lawyers.

The scandal has wiped almost £300m from Ferrexpo’s market value after Deloitte raised concerns over $33.5m (£26m) in payments to Blooming Land, which carried out the mining company’s corporate social responsibility programme. The charity is linked to Kostyantin Zhevago, Ferrexpo’s founder, chief executive and largest shareholder.

Deloitte had on Tuesday issued a qualified opinion alongside Ferrexpo’s twice-delayed annual report, saying it could not determine whether the charitable donations had been used for legitimate activities. Deloitte also had concerns that the charity was controlled by Zhevago.

Ferrexpo paid Blooming Land $24m in 2017 and $9.5m in 2018. In total since 2013 the company has paid $110m to the charity, which was meant to be used to support diabetes prevention, eyesight care and care for the elderly.

Ferrexpo said it stopped payments to the charity in May 2018, but three months later Deloitte found “a number of irregularities” which included “inconsistencies in copy bank statements provided by the charity”. Blooming Land partly blamed the inconsistencies on the June 2017 cyber-attacks on Ukrainian financial institutions, but Deloitte said it had concerns over the credibility of that claim.

Ferrexpo said Zhevago did not have significant influence over Blooming Land “as defined under applicable accounting standards” or listing rules.

Two non-executive directors of Ferrexpo resigned on Friday, piling extra pressure on the company. Mary Reilly and Bert Nacken previously chaired the company’s audit and remuneration committees, and both served on the four-member committee which was eventually tasked with overseeing an investigation into the discrepancies.

Ferrexpo said it could not guarantee that no money had been taken for illegitimate purposes. Steve Lucas, its chairman, said: “At this stage we cannot conclude as to the ultimate use of all of the funds by the charity.

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“While there are indications that some funds could have been misappropriated, further work is required before any final conclusions can be drawn and the board would like to make clear that to date no conclusive evidence of misappropriation of funds has come to light.”

Ferrexpo shares have traded on the London Stock Exchange since 2007. It was a member of the FTSE 100, but the company was demoted from the blue-chip index as iron ore prices fell.

Deloitte declined to comment further.