The man in charge of a Shropshire construction giant which collapsed with the loss of more than 500 jobs has claimed he could have been a victim of fraud.

Businessman David Unwin, the chairman of Wrekin Construction when it collapsed earlier this year, bought the company with a ruby valued at £11 million in 2007.

But Mr Unwin says he is not an expert in gemstones and could have been duped over the ruby.

Mr Unwin yesterday admitted that he “knows nothing” about the valuation of gemstones, despite selling the Gem of Tanzania, dubbed the Wrekin Ruby, to the construction firm in exchange for £11 million of shares.

The sale of the ruby, from Mr Unwin’s Tamar Group, helped to transform the balance sheet of Wrekin Construction which showed a profit of £1.6 million by the end of 2007, from an £8.2 million loss the previous year.

Mr Unwin claimed on the BBC’s Inside Out programme last night that he had relied on a valuation for the ruby gemstone from a third party, which has since turned out to be a forgery.

Wrekin’s company accounts show an £11 million valuation of the stone, which was previously valued on its parent company Tamar’s accounts at £300,000.

Mr Unwin added: “I did not believe the gem had increased in value 30-fold in 12 months.

“I believed it to be worth much more when I bought it,” he said.

“Was I naive in the face of making a huge profit? Almost certainly.”

He added: “Have I myself been the victim of a fraud in relation to the gem? Quite possibly.”