The Conservatives have called for the Department of Trade and Industry should appoint independent inspectors to investigate the collapse of Transtec, the engineering firm whose directors included a former Labour minister.

Shadow trade spokeswoman Angela Browning has written to the Trade Secretary, Stephen Byers, urging him to "uphold the integrity" of the department through a independent inquiry which will be made public.

TransTec, the engineering company in which former paymaster general minister Geoffrey Robinson is a major shareholder, called in the receivers last month.

The chief executive and finance director both resigned after disclosing the company had an undisclosed claim for $18m (£11m) from its largest customer, the Ford Motor Company.

'False market'

In her letter to Mr Byers, Mrs Browning said: "The concealment of such a claim from Transtec plc's auditors, public investors, creditors and employees raises the spectre, in a publicly quoted company, of false accounting, the making of false statements to Transtec plc's auditors, and, most obviously, the creation of a false market in Transtec plc's shares.

"The question of who knew of this claim, who participated in its concealment and who stood to benefit from its concealment, will thus be of no small significance."

Transtec was formed out of company in the Robert Maxwell empire, of which trade minister Helen Liddell was once an employee, the Tories have been quick to point out.

The Conservatives also point to the fact that another minister within the DTI, Patricia Hewitt, once worked for Andersen Consulting while Transtec have appointed Arthur Andersen as administrators.

Mrs Browning also pointed to the fact that a DTI inquiry into another company, Hollis Industries, that Robinson was involved was not made public.

'Whiter than white'

"All this makes it very important for the DTI to be seen as whiter than white," said Mrs Browning.

Along with the letter to the DTI, the shadow chief secretary to the Treasury David Heathcoat-Amory has written to the Stock Exchange to express the Conservative's concerns over the inquiry into Transtec.

The trade secretary has powers to appoint independent inspectors under the 1985 Companies Act.

Mrs Browning said it was the only way "the web" could be resolved as independent inspectors have a wider remit than receivers.

She said: "I believe the only way the secretary of state can respond is to exercise his powers for an independent inspectors' inquiry."