A TRUST set up by the architect Lord Foster for the benefit of his staff is the subject of an official inquiry into its multi-million-pound winding up.

Foster’s 900 employees helped him make a £295m fortune changing the skylines of London, New York and Hong Kong, but now some of them are seeking a clear explanation of how the trust’s assets were divided.

When it was closed, it paid out an estimated £3.6m to staff although it had owned nearly 50% of Foster’s £300m firm.

The firm’s recent buildings have included the new Wembley stadium, the “gherkin” skyscraper in the City of London and the world’s largest airport in Beijing. One current project is a tower at the new World Trade Center in New York.

But Chris Cook of the Financial Services Commission in Jersey said this weekend that it is “making inquiries” into the trust, which is registered in St Helier.

The inquiry has been sparked by a series of financial transactions intended by Foster, 71, to change the ownership structure of his practice in preparation for his retirement. The architect recently increased the number of shareholders from four to 14, although he retains control.

The regulator’s move follows a string of complaints from disgruntled employees. It will examine the closure of the offshore trust in preparation for the sale last month of a minority stake in Foster & Partners to 3i, the private equity investors, which earned Foster a reported £100m.

Six employees have complained to the Employee Share Ownership Centre, an employee rights organisation.

They allege they were told little by the trust about how the sum they received was calculated or their rights to the trust as Foster workers.

“There are a lot of disgruntled people,” said one senior employee who recently left the company. “People have told me it was like sitting in a slow motion car crash. Nobody knows what is going on. The lack of transparency is breeding mistrust and discontent.”

The firm’s staff earn an average £40,000 while Foster, the chairman, is the highest-paid architect in Britain with a salary of more than £2m a year. His perks include use of a private jet.

The trust is private and produces no publicly accessible accounts. Future accounts published by Foster & Partners could give an indication of who was entitled to the proceeds.

“It raises the question of where all the money has gone,” said Mike Warburton, a senior partner at Grant Thornton, an accountancy firm, who has scrutinised the accounts. “I can’t answer that, but I can well understand why the question is being asked.”

Foster, originally from Man-chester, established his practice 40 years ago, since when he has expanded to become one of the world’s most powerful architects. Foster’s tight control of the firm’s ownership reflects his dominating management style – no other architect has been allowed to become a significant shareholder in the firm.

In 2003 his partner Ken Shut-tleworth, nicknamed “the pen”, left after the pair squabbled over who produced the idea for the gherkin – the London headquarters of SwissRe, the reinsurance giant.

The decision to wind up the employee benefit trust emerged earlier this year when employees at Foster’s offices received a letter stating that all money held by the trust would be distributed among eligible staff. Cheques of up to 10% of annual salary were attached. Before tax and national insurance, the average payout was £4,000.

The reason for the apparently low figure may lie in the trust’s structure and internal rules, which are not publicly available.

Foster & Partners declined to comment this weekend beyond saying that it was the trust not the firm that was being scrutinised. The trustees, based in St Helier, declined to comment.

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