A crooked gem dealer who conned elderly investors into buying over-priced diamonds with their life savings as part of a £1m fraud is facing jail.

John Bishop, 32, cold-called scores of victims to promise sky-high returns on their money – including a retired police officer who spent £140,000 on coloured stones worth little more than £10,000.

The year-long scam was masterminded by Bishop’s friend Adam Simmons, 28, and was based at the No.1 Gems firm in Hove.

Simmons, of Booth Street, Old Swan, Liverpool, was jailed in September last year along with his father Michael, 54, of Lion Hill, Stone Cross, Pevensey, brotherin- law Adam Leach, 30, of Hambleton Close, Eastbourne, and colleague Lee Miller, 33, of Sackville Road, Bexhill.

Bishop, 39, of Queens Road, Felixstowe, Suffolk, denied involvement in the fraud but was convicted of conspiracy to defraud and transferring criminal property after a trial at the Old Bailey which ended yesterday.

The court was told Bishop operated from his sales office in Marbella, Spain.

No1 Gems was set up in late 2011 and conned a total of £1m from investors before it was raided by police in September 2012.

Jurors were told victims of the scam were sent glossy brochures and told that HSBC bank had agreed to buy the entire stock of No1 Gems for £15m.

All the gems had been purchased from a diamond catalogue before being given huge mark-ups.

Prosecutor David Durose said: “Basically, No1 Gems were engaged in what is known as a boiler room fraud.

“It is a specific type of fraud in which individuals are targeted with cold calling and pressured into making purchases of items such as shares, equities or financial instruments - or in this case, diamonds.”

One victim initially agreed to buy one 0.26 carat green diamond for £5,598 in March 2012 after being told he could make annual returns upwards of 20 per cent.

In reality the diamond was only worth £350 and would still be worth less than £1,000 after three years at that rate.

Mr Doorbar bought a total of nine stones from the firm and used the last of his savings for his final £9,000 purchase.

Bishop is due to be sentenced at Woolwich Crown Court on September 15.