The ruby gemstone had been valued at £300,000 but finally sold for £8,000.

Two directors of Shifnal-based Wrekin Construction Company Ltd had reason to doubt the sky-high valuation of the gem but allowed the figure to be included on its balance sheet, turning the firm from a loss-making business into one making a profit.

Now, those men – Paul Unwin and Nicholas Ibbotson – have accepted long-term bans as directors.

Investigators from the Insolvency Service said Mr Unwin listed the ruby, known as The Gem of Tanzania, as an £11m asset on the firm’s books in December 2007, despite the fact that he had valued it at £300,000 four months earlier.

The 65-year-old, who lives in Widnes, has signed a 10-year disqualification undertaking while Mr Ibbotson, 56, from Sutton Coldfield has made a similar move on a seven-year order.

Wrekin was a large civil engineering company based in Shropshire that was set up in 1960.

By March 2007 it recorded a £7.6m trading loss despite having an annual turnover of more than £100m. It was bought by Unwin in June of that year, six months before he transferred the Gem of Tanzania to it from another of his companies – Tamar – where it had been recorded as a £300,000 asset in return for shares.

But immediately after the switch, it was listed in the Wrekin accounts as being worth £11m, allegedly based on a valuation in Italy four months previously. Wrekin Construction Company Ltd collapsed in March 2009 with the loss of more than 500 jobs while owing more than £45m.

When administrators tried to sell the gem, they found the valuation certificate was a forgery.