In 2005, Phil Stanley and Sue Lyons opened their Nelson home to Gerald Shirtcliff, the construction manager of the Canterbury Television building.

Now, following a Press investigation, the couple have learnt their guest was an identity thief who falsely claimed he was a qualified engineer. 

Shirtcliff took the identity of English engineer Will Fisher, whom he met in South Africa in 1968, and used his qualifications to launch his own engineering career in Australia. 

In 2005 he was sentenced to 20 months' jail for forging GST receipts to make a business he sold to a Queenstown couple appear more successful than it was. 

That became home detention after two weeks, when Stanley and Lyons said they'd take him in. 

"He convinced us he was innocent," says Stanley. 

"We felt sorry for him. He was like Father Christmas. The white hair, the big smile, the charming old pensioner."

Shirtcliff told them he was due a $900,000 pension from his time as a manager at a Ford plant in South Africa. He stayed for 20 months, helping out in the couple's Sydenham automotive repair business. 

"He was an absolute master for charging for things he didn't fit. I had to tell him that was not the way I operated," Stanley says. 

An inventor specialising in alternative fuels, Stanley had a Honda Civic running on ethanol by the time he was 27, and while Shirtcliff was with them, he was testing a dual-fuel system for diesel engines he had developed over a decade. 

A test engine in his workshop was running on four different fuels, and he would later get it running on cow effluent. 

Shirtcliff showed interest and although Stanley normally made people sign confidentiality agreements, he made an exception for Shirtcliff and explained it all to him. 

When Shirtcliff's home detention was up, he returned to Australia. 

"As soon as the bracelet was off, he was off to the airport, no goodbye, no thing," says Lyons. 

One his return to Brisbane, Shirtcliff touted dual-fuel diesel technology to investors, and got a $1000-a-week retainer to develop it. 

Stanley knew nothing of the deal, which Shirtcliff did not mention when he called from West Australia to talk about discovering a uranium field. 

"I couldn't believe I had a conversation with him six months after he went back and ... he failed to mention he was working on a fuel system," he says. 

By September 2007 a company connected to Shirtcliff had filed a world-first patent in Australia for a dual-fuel system for a diesel engines - strikingly similar to Stanley's. 

"Even if the description is a little different, we gave him the idea and there is no way he had the technical knowledge to come up with it himself," Stanley says. 

"I couldn't believe it when I heard [from The Press] that he had taken our idea. But that would be him."

The couple say they will challenge the patent. 

"All my life I've been robbed of my ideas," Stanley says. 

- © Fairfax NZ News