There's nothing grey about a certain corporate everyman

The Aggreko chief executive's dexterous use of language usually ensures any conversation is undertaken with a hint of a smile hiding somewhere even when serious things are being discussed.

That sense of fun shines through his online postings, which make little reference to his role at the head of one of Scotland's most successful companies.

Ensconced in a conference room at the Grand Central Hotel in Glasgow, where the company's annual general meeting was held this week, Mr Soames was able to reflect on some of the memorable moments of his 11 years at the head of the temporary power supplier he is leaving in a few days time.

Perhaps picking the opening ceremony of the London Olympics does not come as much of a surprise but as ever the anecdote is delivered with a flourish and also brings in a bit of royalty and potential terrorism for good measure.

Mr Soames said the knowledge "that every watt of power that was in that stadium came from Aggreko" was a very proud moment.

But he indicated there were concerns the ceremony may have been disrupted. Indeed he was made aware of a potential threat to the power supply in the south east of England which was being taken seriously by government.

Mr Soames said: "Having asked the question was it safe to proceed with the opening ceremony and take the Queen there, then say 'You betcha, that is what you paid for' was memorable. [Then] to see the stadium, to know what was going on and know that we were doing our job."

In general terms Mr Soames, the Eton educated grandson of Sir Winston Churchill, takes pride in the way Aggreko has been able to react to disasters around the world ranging from hurricanes in the United States, flooding in Australia and the Japanese tsunami.

He said: "[We] try to make things a little bit better and restore power where there was none."

Alongside that he is hugely enthusiastic about the work Aggreko has done and continues to do in supporting emerging economies.

He said: "Essentially we are bringing electricity to them and allowing them to grow their economies

"It has been hugely rewarding for me. I am very passionate about the emerging economies. I find them endlessly fascinating.

"You see over the last 10 years how parts of Asia, Africa and South America have absolutely transformed themselves.

"It has been while I have been working in Aggreko that we have gone from there being virtually no mobile phones in sub-Saharan Africa to there being more there than in the whole of Europe."

Part of that work can sometimes involve deploying equipment in areas which have been devastated by war or cut-off from external influence for a long time.

Mr Soames picks Yemen as an example of somewhere he found satisfaction in Aggreko bringing power to a country.

Alongside the business decision he clearly felt a moral obligation to see that contract through and said: "[Then] perversely [we saw] in some quarters huge opposition to people having power because it meant they could study, and particularly women, could study at home at night.

"There were forces who did not want to see the education of women in Yemen. By bringing power we brought light, televisions and an open-ness to the outside world which was a remarkable thing to be involved in."

Although a major factor in the success of Aggreko (the share prices was hovering around £1.50 when he was appointed), Mr Soames is quick to rule out the idea of the all powerful and omniscient chief executive.

Instead he takes great pains to point out the "orange blood" culture which he believes runs through the business in all the outposts it operates in.

He said: "It is possible to overstate how far companies can be exceptional but as far as they can be then I think Aggreko has an exceptional group of people.

"This thing about focusing on getting the right people in place is absolutely the key."

Yet all good things must come to an end. On Wednesday he formally leaves Aggreko, where he has been since July 2003, before taking up his new job as head of Serco the following day.

As one of the longest serving FTSE100 chief executives Mr Soames' eventual departure has been long planned for.

He said: "I think as a CEO one of the greatest services you can do to a company is to know when to go. I have served under the great Lord Weinstock for 16 years at GEC and I think he probably stayed too long and I saw the consequences of that.

"I think 11 years is a long time to serve. I'd had various discussions with the board about this. It was known at the last strategy review we did, which was last year, that I wouldn't do the next one.

"We were in sort of an area of time between the last strategy review, the reorganisation into a regional structure, a whole lot of heavy lifting going on and I felt very confident about the management team that is here now.

"If you take the view that chief executives are like uranium and become toxic then you are better off disposing of yourself and so I just think the time is right."

The thought of stepping back from front line executive duties was not a consideration.

Mr Soames said: I'd like to be a CEO again. I don't want to retire to a portfolio role of non-executive [directorships] at 54. I feel I have another big job in me."

He describes Serco as a "very great company in a very different sector in very different condition" from Aggreko but declines to comment further on his plans until he is actually employed by the outsourcer.

However he is confident his skill set has improved during his tenure at Aggreko and remains glad the board had faith in appointing him following an abrupt departure from software company Misys.

He said: "Hopefully I am better at being a CEO now than I was 11 years ago.

"It was a great act of faith by the previous board to hire me as I had been fired from my previous job and been unemployed for a year.

"There were many reasons not to hire me but they took a risk and I will be ever grateful for that."