Each of the four men portrayed has had an influence on the family-owned firm: bakery founder and Boyd's grandfather Thomas Tunnock, Boyd's late father Archie, who expanded the business into catering, his late elder brother Tom, who died of MS, and Robert Burns, with whom Boyd shares a birthday.
"They probably think I'm not doing well enough," laughs Tunnock, as he considers what these figures would make of his contribution to the company, which now has a turnover of £32 million and exports to more than 30 countries.
Although he officially retired 14 years ago at the age of 65, managing director and majority owner Tunnock has been at the helm for 30 years since the death of his father. "He left me money in the bank. I've still got money in the bank. Everything we spend is our money. We've never borrowed money."
He takes out a huge desk calculator to help him quantify the company's latest market – its inaugural order bound for South African supermarkets departed just before Christmas. "That's 20 pallets or 1080 cases, 32 by six. In single teacakes, that's 207,000."
Export sales manager Alan Burnett, who replaced Tunnock's youngest daughter Fiona eight years ago, is just off the phone from a buyer in Libya. He joins the boss in his office for a spot of international number crunching.
Irish supermarkets now want larger display boxes containing 24 teacakes and snowballs to meet customer demand. Its biggest export market continues to be Saudi Arabia, followed by Canada, which was the company's first export customer in 1957 and explains the English or French language options on the company's website.
Australia is blossoming now that the company's products are stocked by Coles supermarkets. Kuwait, meanwhile, can't get enough Caramel Logs. "And Dubai wants a 40 [ft container]," relates Burnett. "Do they? No!" exclaims Tunnock in response to the news 700,000 chocolate-covered logs will soon be shipped to the UAE.
"This year we'll do about £7 million turnover export-wise, which is 50% up on last year. It dipped a bit last year," adds Tunnock of the impact of the economic downturn.
Every year Tunnock's sales staff attend the ISM confectionery trade fair in Cologne, but can't seem to shift so much as a snowball on the continent. As such, Tunnock admires David Cameron's decision to take Britain a step back from Brussels controlling the purse strings. "I'm not frightened to say that I'm a Unionist. But I'm actually a Nationalist British. I don't want Scotland to stand alone. I want the United Kingdom. That's the strength: the United Kingdom. We get enough say in the Scottish Parliament, doing what they're doing."
Is he impressed by the Scottish Parliament?
"I think they're doing all right. Alex Salmond is okay," said Tunnock, who would like any referendum on Scottish independence to be held sooner rather than later, as he believes uncertainty is bad for business.
An interview with Tunnock, who turns 79 this week and has an estimated personal wealth of some £30 million, isn't what you might call typical: he rattles off anecdotes at a rate similar to the speed Caramel Wafers are wrapped.
Before even settling into his seat, he's off: he doesn't want to talk biscuits. No, he wants to talk about how The Herald – which he has delivered every morning – should have more coverage of The Tour of Mull Rally, which Tunnock's has sponsored since 2005, and the Scottish Series Yacht Regatta at Tarbert. On a recent West Highland Yachting Week sail, he did all the cooking on board the 38ft yacht Lemarac (Caramel backwards) for up to 12 crew and guests at a time.
His office is strewn with model yachts and photos depicting his days as a champion rally driver. He points to one favourite photo of him taken on a grass hill in Edinburgh with all four wheels of his MGA Twin Cam off the ground. He famously auctioned one of his Rolls-Royce cars, a brand new peacock blue Silver Seraph, for £160,000 in 1998. Proceeds went to his three favourite charities: the Salvation Army, the Royal National Lifeboat Institution and Malin Court residential home for the elderly in Turnberry.
It was also through a love of cars that he met Anne, his wife of 54 years. Tunnock's 17th birthday present was a powder blue MG TC, bought by dad Archie for £525 – plus a few bottles of rare Johnnie Walker to bypass the two-year waiting list – from Cecil McLay's garage in Kirkintilloch. As a thank you, his father invited the McLay family to dinner, including their daughter Anne. Boyd and Anne began courting that September after a pal bet him a half crown he didn't have the nerve to ask her out.
During the seven years before they married in August 1957, Tunnock worked in the factory during the day while learning his trade as a baker by attending nightschool three times a week at Hamilton Academy, qualifying in 1954. He proposed to Anne during his two-year national service in the Army Catering Corps. He was posted to a cookhouse at Bicester Garrison near Oxford and within a year progressed to corporal, becoming a sergeant six months later, in charge of feeding 600 hungry mouths.
He treasures photos of his dad standing next to a Caterpillar tractor, another icon of Lanarkshire industry, in Mesopotamia. Archie returned from three and a half years' service in 1920 to hear at Glasgow Central that his father Thomas had passed away and that his dying wish was for Archie to grow the business.
"Morally, my regret about the army was that I wasn't abroad," said Tunnock, who was named a CBE in the 2004 Queen's Honours list after receiving an MBE in 1987. "I would have loved to have joined the Paratroopers. I'm a bit more blasé now. In those days I was quite quiet. You develop over the years."
In the last few months, Tunnock has had a busy calendar of speaking engagements around the country. He and Anne have three daughters: eldest daughter Leslie, Karen, who runs the day-to-day business with sales manager husband Fergus Loudon, and youngest daughter Fiona, who also remains a director after giving up her job to raise a family.
Aside from cars, Tunnock's other extravagance, a Rolex watch bought in 1965 for £52, hasn't been worn much since he suffered a "heart flutter" on holiday in Antigua seven years ago. "I started spitting up blood," said Tunnock, whose heart attack was only diagnosed after he returned home. "I remember someone telling me, if you've had a wee heart flutter, you throw your watch away because you're constantly saying 'Look at the time, I'm late'."
It meant he had to give up windsurfing ("like driving a racing car") and for six weeks he couldn't drive his Rolls the 300-yard journey to work, either. He now relies on one other personal concession to modern technology to tell the time. "It's just an ordinary wee phone. I don't have one of these iPhones. They don't last long. I like one that lasts. I see Nokia are bringing one out and the battery will last for a month. That would be great."
Cups of tea brought religiously to Boyd at 9am, noon and 4pm are served using a Tunnock's-branded sugar bowl and milk jug from 1938 and 1948 respectively and dating from the heyday of his father's catering business. Boyd steered the company away from catering and baking: in 1994 he made 81 workers redundant when Tunnock's stopped making wholesale cakes and focused on biscuits. Yet he continues to operate the Tunnock's bakery on Uddingston's Main Street, which his grandfather opened in 1915, despite it making "a glorious loss". "It's only baking for one shop," he states. "But it's history. There's something comes out it. You've got that to bring you back."
The company made headlines in September 2010 when members of the Unite union took part in industrial action. Mention of the strike provokes little more than a shrug from Tunnock, whose company employs 550 people. "It didn't bother me," he said. "The first one I can remember was 1972. Then I think the next one was 1990. We generally have them every 10 years. You know, it's the only time in the year staff have got their say as to what you pay them."
He estimates he signs cheques for £2 million annually for new plant equipment. He has ordered a new cooling tunnel and a machine that can wrap 500 Caramel Wafers a minute, the latter a fitting tribute to the wafer's 60th anniversary this year.
In bygone days, when teacakes were piped by hand, it took 23 staff to make 3000 boxes a week. Now they can produce 99,036 a week on its predominantly-automated production line. They have only one own-label customer, having made snowballs, teacakes and caramel wafers for Newcastle-based Ringtons Tea for 42 years.
Tunnock spends 80% of his waking hours in the factory and doesn't plan on retiring properly until he's 100. His personal challenge every day is to beat his engineers at their own game – spotting the improvements that can be made in the efficiency and accuracy of the machines. If that means lying on his back on the factory floor, or squeezing under wrapping equipment, then so be it.
Given that he turns 80 next January – with a birthday bash planned for the Hilton in Glasgow – wouldn't his wife prefer that he finally bid farewell to the 6am alarm calls of a time-served baker? "Naw, I'm very good to her," he smiles. "I'm home generally by six o'clock. I'll take her anywhere she wants to go. She's quite happy."
LIFE AND LOVES
Being able to say to people that I originated the teacake.
I don't have any.
Favourite holiday destination?
Loch Torridon. It's super. The Torridon is a quiet hotel – you can sit looking at 300ft mountains.
Three Coins in the Fountain.
The Bee Gees or Frank Sinatra.
Last book read?
David Niven's life story.
Best advice received?
You've got to believe in God. You've got to believe in something.
My father, and Andrew Carnegie, who was a great philanthropist. I believe in helping others.
Perfect dinner guest?
At a Yorkhill fundraiser I bought a dinner for two with Susan Boyle, pictured. She's an honest, down-to-earth person.