Donald Wilson is giving his first interview after 25 years working alongside Sir David Murray and explains: "I would never have competed with David, it is not my style.

"Now I represent a substantial business with strong partners it's important for me to represent them."

Mr Wilson, 50, stepped down from the board of Murray International Holdings (MIH) 13 months ago to work on the buy-out of one of its overlooked but most promising assets, Premier Hytemp, an oil and gas engineering specialist which he had nurtured for many years.

Premier hiked sales 15% to £60 million last year and achieved a £3m profit turnround to make £1.5m pre-tax, and has been lauded by Scottish Enterprise as a flagship of international growth.

It has bases in Calgary (Canada), Houston, Singapore and Dubai, as well as Sheffield and Aberdeen, but its manufacturing is done largely at Newbridge, Edinburgh.

"We had Michael Moore [Scotland Secretary] come out to see us," Mr Wilson says.

"He wanted to see an ambitious Scottish business, and he was quite surprised to see an engineering company on the outskirts of Edinburgh."

On his ambitions, Mr Wilson says: "I would like to think that our plan will double the size of the business over the next three to five years."

He and two other executives completed the £34m deal with backing from Dunedin last St Andrews Night.

"It was at Dickson Minto's offices and as soon as we finished the signing and had a wee glass of champagne, the fireworks went off and I thought 'I hope this is a good omen'."

It marked the end of accountant Mr Wilson's 25 years sharing the highs and lows of Sir David's empire – including nine years on the board at Rangers.

He said: "I did a lot of difficult things with the company over the years and I am very proud of it. It was a very difficult time for everyone at MIH, it was a perfect storm – steel, property, football, and our bank going bust, but we fixed things - I often wondered what would have happened if Bank of Scotland hadn't gone down."

Mr Wilson is unstinting in his praise of the Bank of Scotland maestros who helped build, and in the early 1990s rebuild, the Murray empire – Gavin Masterton, the late Iain Robertson, and the reviled Peter Cummings, whose treatment he says has been "unfair". He adds: "Any time I met Peter I thought he was a very solid, sound banker."

When in 2009 Mr Cummings disappeared, the then chief executive of MIH had to beat a path to the door of Lloyds in London.

"What happened was quite tricky for me personally," he recalls.

"In the past they had encouraged us to take on businesses, turn them round and sell them, with Lloyds there was an independent business review, we had to introduce ourselves, and they said here is a process."

But then came the opportunity. "Lloyds said there is a specific part we need you to fix and take responsibility for."

Mr Wilson had driven the recent growth of engineer Premier Alloys, acquired by MIH in 1985, overseeing a clever merger in 2008 with oil and gas specialist Hytemp, part of another Murray acquisition Sheffield-based Hillfoot Steel.

"When we sold Murray International Metals in 2006 it opened that business out, we had some cash to invest and I thought it was underachieving relative to its market-place though it had a pretty good competitive advantage. I saw a business that manufactured, and was a bit sleepy.

"Over the years with David as an entrepreneur, things suddenly appeared, some of them worked, some didn't, this one had probably got lost in the roundings, and I got control of it.

"We did trade with Singapore and we bought a similar business there."

Step forward Donald Wilson, entrepreneur.

"I like to think I have picked up a bit along the way.

"I have learned a lot from mistakes like the Sunday Scot and some of the other businesses, but I have also been around enough in crises to understand what you need to do.

"As the financial man it's easy to take a negative position and I remember David saying to me once: 'If you are so smart what are you going to do?' To be creative is quite difficult."

Premier Hytemp raced to record orders at the end of 2008, but then came the next challenge. "Its market collapsed, it just fell off the edge of a cliff, but so did everyone in the industry.

"But the prospects were very very good, the capex spend in our market was very high and there was a lot of interest in the oil and gas sector. It recovered, the market started to come back, and we were in a good position to benefit."

He explains: "We buy in stock – metal, alloy bars – machine it, put it through a heat treatment process and a rigorous suite of tests, and supply the onshore and offshore oil and gas market.

"Our principal products are wellheads and 'Christmas trees', the stuff that sits on top of the hole in the ground. It's a really critical piece of kit.

"When Deepwater Horizon (BP) kicked in, that created a bit of a ripple in the market and that has made our process very important."

By 2012 Mr Wilson was running the business full-time. "It was offered to me and I said yup, I can have a go at that, it seemed to be a natural progression."

The deal gave Mr Wilson, finance director Mark Gold and Singapore-based operations director Doug Harrison a significant stake in the business alongside Edinburgh's buy-out specialist.

"We went out to everybody and Dunedin emerged. Some of them are personal friends. We got a tremendous response but Dunedin emerged as a very strong contender."

Now the man who started as David Murray's number cruncher in 1987 is leading the growth strategy of his team's hi-tech business, with his next target the market in Brazil.

He says: "In Scotland we seem to have lost the David Murrays and the Tom Hunters.

"I am not saying we need celebrity businessmen, but what we do want to see is companies emerging with ambitions on a global scale."