The owner of Patisserie Valerie has been plunged into financial crisis after it revealed a multimillion pound accounting black hole and that its main trading subsidiary was facing a winding up order.

The 92-year-old cake chain, which has more than 200 stores, halted trading in its shares as it revealed “potentially fraudulent” financial irregularities that, according to Sky News, could amount to more than £20m.

Just hours after the suspension, Patisserie Holdings said its board had been unaware HM Revenue and Customs had filed a winding up petition at the high court against Stonebeach over an unpaid £1.14m tax bill.

Patisserie Holdings is listed on the Aim junior stock market and has a market valuation of nearly £450m.

The company’s finance chief, Chris Marsh, who was one of two directors of Stonebeach, has been suspended from his role. Marsh joined the company in 2006 and in July made a near £700,000 profit, after selling shares awarded from a long-term incentive scheme.

Announcing the share suspension on Wednesday, Patisserie Holdings said it had been notified of “significant, and potentially fraudulent, accounting irregularities and therefore a potential material misstatement of the company’s accounts”. It said this had significantly affected its cash position and could lead to a “material change” in its overall financial position.

It later issued a statement saying that its board of directors had only just become aware of HMRC’s action against Stonebeach. The petition, which was filed on 14 September, could lead to the subsidiary being declared insolvent and closed down. The action was advertised in the London Gazette, the official public record, on Friday and is expected to be heard in court on 31 October. The second director of Stonebeach is Paul May, Patisserie Valerie’s chief executive.

The serial entrepreneur and Sunday Times business columnist Luke Johnson is chairman of the holding company. He is the group’s largest shareholder, with a 37% stake – worth £165m at the time the shares were suspended.

On Wednesday, Johnson said: “We are all deeply concerned about this news and the potential impact on the business. “We are determined to understand the full details of what has happened and will communicate these to investors and stakeholders as soon as possible.”

An insolvency expert said the winding up petition would enable other creditors to call in their debts and could prompt banks to freeze Stonebeach’s accounts and credit insurers to withdraw cover for its suppliers. The expert said all transactions from 5 October would now be subject to scrutiny and the directors could potentially be held accountable for trading while insolvent.

Pattiserie Holdings said it was “in communication with HMRC with the objective of addressing the petition.

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Johnson is understood to be driving an internal investigation, while PricewaterhouseCoopers is believed to have been called in to carry out a review of accounts. Patisserie Holdings’ auditor, Grant Thornton said it would be inappropriate to comment because of its duty of client confidentiality.

It is expected that the regulators the Financial Reporting Council and the Financial Conduct Authority will both examine the issues at Patisserie Valerie. The Serious Fraud Office could also look into the matter. All three bodies declined to comment on whether they had yet been in touch with the company.

In May the firm reported pretax profits of just over £11m for the six months ending on March 14 – up 14% on the previous year. Revenues were up 9% to just over £60m, it said at the time.

Alongside its store estate, Patisserie Valerie has a partnership with Sainsbury’s, with branded counters present in the supermarket.

The company started in 1926, when Madame Valerie, a Belgian national, opened a shop in Soho, central London. In 1987 it was bought by the Scalzo brothers, who opened several more outlets. Johnson’s Risk Capital firm bought a controlling stake in 2006, and floated the business on the stock market in 2014, with the shares priced at 170p. The shares were trading at 429p just before they were suspended.

The problems at Patisserie Holdings come a little more than a month after Johnson published a newspaper column with a “beginner’s guide to tried and tested swindles”. In the piece, he said: “even clever investors sometimes fall for the most ambitious fraudsters”.