Until recently, it has also been top secret.

It was here, before umpteen stealth servings of roast beef, that Waddell and his son-in-law Robert Etherson – not to mention their respective families –

hammered out the idea of launching a new company, Energen Biogas, and building Scotland’s first industrial-sized anaerobic digester, which will also be the biggest of its kind in the UK.

At the same time, it was also an idea that provided the opportunity Etherson had been waiting for to return to his beloved west of Scotland and for Waddell to pass on his years of business expertise and experience to his family.

The two men are now poised to become the greenest team in Scotland.

In spite of its ominous-sounding name, an anaerobic digester is not a creature from a 1950s B-movie with an evil plan to gnash out of existence all human life on Planet Earth.

On the contrary, anaerobic digestion is an Earth-saving process, by which plant and animal waste is digested in tanks by micro-organisms, which then release methane that can be used to provide heat and power, in other words, pure “green” energy.

The process of anaerobic digestion is the breakdown of microorganisms into material that is biodegradable without oxygen.

Originally the process was relatively expensive, requiring significant technical expertise, and there was little demand for its use except for industrial types of application.

More recently, the process has been perfected and costs have been lowered considerably, enabling it to be seen as a viable source of alternative renewable energy.

Producing renewable energy from biodegradable waste, which has gained the support of Friends of the Earth, helps tackle climate change, instead of contributing to it through landfilling and incineration.

Behind every business idea is a story, and the bones of this one goes back to the dinner table in Paisley, where the idea was developed slowly and determinedly amid secret servings of Sunday lunch, heated conversation and impatient family members, who in the end begged the pair to just get on with it.

Over soup and bread, beef and chicken, cakes and pies – all of which can be anaerobically digested – Waddell and Etherson thrashed out a plan to build an organic waste plant and electricity generator smack in the middle of central Scotland. And as industrial waste disposals and energy plants go, it would be the greenest of the green.

The Herald met them in a restaurant in the centre of Glasgow recently, and while there was no roast beef, the topic of conversation had changed little.

The pair were as fired up as ever about the idea of anaerobic digestion. The primary problem, however, was not the construction of this giant waste manager and power generator, or even raising the cash in the middle of a credit crunch. The big problem was how to keep an £8m facility in Cumbernauld, North Lanarkshire, where they intend to transform 60,000 tonnes of kitchen and farm waste each year into “green” electricity for 4,000 homes, a secret – even at the idea stage.

Waddell, who at the time was still business director of Rolls Royce in East Kilbride, could not utter a word about the plan until he retired in August 2008.

Etherson also had to keep mum until just a weeks ago. He was working as the chief executive of Arbroath-based Abbey Fruit, one of the UK’s leading fruit packers, and dared not tell his employers until he was sure of his next step. He had a family to support – three children and his wife, Jacqueline, Waddell’s eldest daughter.

And so Waddell and Etherson became something more than in-laws. They became partners-in-law in a secret pact known only to themselves and their families.

Waddell, who was with Rolls-Royce for 34 years, had business connections and the experience. He is also head of the west of Scotland regional advisory board of Scottish Enterprise, and his prime motivation – like any proud father and grandfather – was to help his family.

“The idea came out of an original intention to open a glasshouse business, given Robert’s knowledge of the produce industry and his position with Abbey,”

Waddell said.

“Years ago, there were large glasshouse businesses throughout the Lanark valley, but the number of hours of sunlight here make it impossible to compete with places like Holland.

“So then we began thinking about organic energy and we moved on to the idea of biomass and biofuels. We could see that energy prices were rising and that biomass was a huge growth area. We also knew it was something the Government was very keen to push forward.”

Etherson added: “We basically Googled the word biomass and hit upon anaerobic digestion. This is a waste management and energy generation system that works like a big cow’s stomach and I realised there was a real opportunity here – for us and for Scotland.” Nonetheless, Etherson also had further motivations.

“To start my own company has been a dream and an ambition since I was a wee boy,” he said.

“But I also had this burning ambition to get back to the west of Scotland – ever since I was a teenager and left home.”

Etherson, who is originally from Torrance, left for a Greek vacation when he was 19 and ended up getting a job with Thomson Holidays before moving to Italy, where he remained for eight years.

He said: “I wanted to see a bit of the world then, but I always wanted to come back.

“I regret that didn’t happen until after my dad died. I remember when I was at Glasgow Airport heading back to Italy and I suddenly had a panic attack. I knew that I couldn’t leave again. I knew that this was where I belonged.”

He added: “I have to say that I’m delighted to be back in Glasgow.

“When I was working with Abbey Fruits, we lived in Carnoustie and Graeme was in Paisley.

“But it was out of those visits to Paisley that the idea for Energen came into being. We used to drive down every weekend and over the dinner table we worked out Energen together.

“After we developed the idea, it was Graeme who went public first.

“I couldn’t say a word because of my position with Abbey Fruits. In fact, it has only been a few weeks that I’ve been able to state my involvement in it. It has all been a big secret until recently.”

In October, press reports emerged that Energen Biogas, which was awarded £2m by the Scottish Government towards the project, had joined forces with Buckinghamshire-based waste management giant Shanks to open the £8m facility in Cumbernauld.

The reports implied that Shanks was the lead project developer.

“We had to do it that way,” said Waddell.

“Robert was still working with Abbey. In fact, his name could not even be associated with the project.

“But in the past few weeks, circumstances have changed and we’re here today to say that it is a Scottish company that is behind the development and that we have

big plans.

“Shanks, in fact, have a 24.9% stake. But actually this whole thing is down to the entrepreneurship of two Scottish guys and, in fact, Robert will be the one running day-to-day business.”

The Cumbernauld plant is scheduled to open in 2010 and Etherson and Waddell envisage opening another 10 throughout Scotland over the next five years.

And what about those Sunday lunches?

The best guess is that they will continue for years to come and any leftovers will end up being anaerobically digested and transformed into energy for the good people of Cumbernauld.