Mild manners that help Clydesdale with tough decisions
A total of 64 branches have been closed - a quarter of its network - as part of a three-year turnaround programme.
About a quarter of the branches have also been closed at Yorkshire Bank, Clydesdale's sister bank within the NAB UK group, with YB also falling within Thorburn's sphere.
Back-office operations have been cut, and overall the reorganisation has seen 1,230 UK jobs go - roughly 600 jobs each at both Clydesdale and YB.
Then in January some of the bank's shell-shocked employees found out that their final-salary pension was going to be cancelled from 1 April and replaced with a less generous average-salary scheme.
The scale of the change reminds me that in the business world it can often be personally friendly executives - which Thorburn is - who push through painful measures. The equally affable Mike Ross did much the same at Scottish Widows amid much abuse.
Reasonableness gives rationalisation a softer face if not making it ultimately more palatable.
Thorburn, a mild-mannered Scot, does not duck the issues. "There have been more than a few sleepless nights. We have had to take some drastic action here," he says.
His emollient yet clear delineation of why Clydesdale and YB could no longer subsidise their final-salary pension schemes was indicative of his style.
The "we" is the 12-strong management committee of NAB UK led by Thorburn's boss, chief executive Lynne Peacock.
Nettles had to be grasped, says Thorburn, and he accepts it must have been difficult for those who were at the sharp end of cutbacks.
Sitting in one of Clydesdale's shiny new Financial Solutions Centres in what could be called Paddington-on-the-Water, west London's new smaller answer to Canary Wharf, he identifies chronic under-investment as the cause of some of the bank's previous problems. That and what he calls "revolving door management syndrome", and an uncompetitive product range.
Thorburn says he believes the fact that the implementation team and the strategy itself have remained unchanged and "transparent" has eased the turmoil for employees.
He is in a good position to know the previous problems. Having joined Clydesdale Bank in 1978 as a graduate trainee, he now recalls the culture then as "grim". He left in 1983 to work for ten years at TSB, returning to Clydesdale in 1993 to help set up a new structured finance unit.
Then came a spell as a divisional manager, running the branch network in east and North-east Scotland. In 1999 he completed the Advanced Management Programme at Harvard Business School.
Thorburn became chief operating officer of the bank in 2002, and took the same role at YB two years later.
"So I have sort of come full circle," he says with a smile, one that is possibly also helped by improving numbers at NAB UK.
The UK arm of the Australian parent group announced a 25 million, or 13 per cent, increase in profits to 219m last month.
Business lending was up 12 per cent at 3.6 billion, and most of the other numbers, from mortgage lending to cost-income ratio, were moving in the right direction.
What has happened strategically at the bank to produce this? A key strand is that Clydesdale has gone into business lending and private banking big-time, mainly through its Financial Solutions Centres.
Second, it has sharpened up its mortgage lending, but Thorburn admits this is meant as a way to cross-sell other more profitable products to people for whom it arranges home finance.
The star turn, one quickly senses from him, is the Financial Solutions Centres. From a standing start under three years ago, he says they "now account for more than half of NAB UK's balance sheet and nearly 50 per cent of earnings".
The centres target the lending needs of small to medium-sized businesses - usually meaning loans of over 100,000 - and then try to cross-sell private banking products to those clients.
There are currently over 80 FSCs, 54 of them under the Clydesdale brand, including 36 in the south of England and 15 in Scotland.
They operate under managing partners with high lending autonomy from head office, lending based on what Thorburn calls chemistry, instinct and networking rather than "scorecard" credit rating.
"Our guys are bankers and we want them to be businessmen," he says. The managing partners and colleagues run their own budgets, as long as they meet the returns asked for by Peacock, Thorburn and other senior management. Deals are also facilitated by well-connected independent chairmen appointed from the great and good of local business people.
Thorburn says: "These are great ambassadors for the FSCs. They are well connected, and can put deals together. It interests them and excites them. They can also act as mentors for our managing partners."
You sense that local autonomy suits Thorburn's natural management style. He says he is not a micro-manager.
He cites the fact that he does not like e-mails. "They don't move the organisation forward. In fact, e-mails I am copied into I don't usually read - they get filed to a separate basket.
"That's because those e-mails that are not directly for you involve you in low-level tactical stuff, whereas I want to keep my head above the parapet."
Thorburn has come a long way from his childhood in Hamilton, where his dad was a civil engineer and his mum was largely at home taking care of him and his sister, the latter now a lawyer.
He is now president of the Chartered Institute of Bankers in Scotland and vice-chairman of CBI Scotland.
Asked the best piece of advice he has ever had in business, he says it is "don't make personal enemies", even in tough, competitive situations.
And the worst piece of corporate advice? "The simplistic saying that there is no place for the middle player, only the big boys and niche players.
"Well, some people in the middle market are doing very very well, while some of the big players are not there any more."
It is probably more than a stab in the dark to infer he may just have Clydesdale Bank in mind.
Born: Glasgow, 1958
University: Glasgow, law degree.
First job: Graduate trainee, Clydesdale Bank, 1978
Family life: married, three children
Last holiday destination: Australia.