The 50,000-square foot factory in Park Royal, west London, is capable of churning out 250,000 sandwiches a day, but Hazlewood is keen to stress that its aim is "mass customisation" rather than simply mass production.
As Europe's biggest sandwich maker and supplier to Boots, Sainsbury's and Asda among others, the company is confident it can match the tastes and expectations created by smaller players.
"This helps the industry because anybody can make a cheese and pickle sandwich at home," says John Simons, the company's UK chief executive. "The more it gets away from what they could make at home, the more people are prepared to go out and try things.
"Obviously, the areas that are not particularly growing are the standard triangular shapes with relatively straightforward fillings, but there's a lot of growth in more exotic fillings and types of breads and rolls. Most people would concede that the quality of sandwiches has dramatically improved over the past few years."
Until recently, the traditional British sandwich, factory-assembled and vacuum-packed, was one of those institutions foreigners loved to ridicule, and with good reason.The fourth Earl of Sandwich must have been turning in his grave.The trend-setting nobleman, who in the mid-18th century famously asked a servant to bring some "cold cuts of beef between two slices of toasted bread" so he would not have to leave the gaming table, might have been more than a little perturbed to see the atrocities committed in his name until very recently.
Lunch was often a culinary ordeal for those not on Conran-suitable expense accounts. With high-street offerings ranging from anaemic strips of bacon stretched across damp squares of starch-white bread, to tinned prawns drowning in day-old mayonnaise, it was a long way from the Earl's robust original, not to mention the extravaganzas available in New York delis and Paris cafes.
"I don't think the British sandwich was anything very great back in the early Eighties," says Jim Winship, director of the British Sandwich Association, which sponsored British Sandwich Week last week. "At one time the British Rail sandwich was a great joke, and I have shuddered at some of the things on offer at petrol station forecourts."
But with the highest per capita consumption of sandwiches in the world - 37 sandwiches bought per person per year - it was only a matter of time before Britain got it right. Towards the end of the Eighties it began to dawn on newly health-conscious Britons, who were also just starting to be exposed to gastronomic innovations in restaurants, on television and during trips abroad, that they were being shortchanged at the lunch counter.
Twelve years ago Julian Metcalfe and Sinclair Beecham harnessed their own dissatisfaction to found Pret-a-Manger, the trendy sandwich chain that now leads the market in terms of innovation, blazing a trail of avocado, sun-dried tomatoes and speciality breads - and shifting 14 million units a year.
"When Julian and Sinclair started, there was a real gap in the market," says Charlotte Fuller, marketing director at Pret-a-Manger. "You could either have a full-blown meal at a restaurant or you could go to a cheap one-off little sandwich place where the service was slow and food wasn't necessarily that good."
Now, however, you can choose Thai chicken or Mexican bean filling, as well as the usual egg and cress (still in Britain's top three choices, along with tuna cucumber and prawn mayonnaise). Only these days the eggs are likely to be free range, the cress organic and the bread satisfyingly unpronounceable.
At Cranks, a small London chain, the focus is firmly on health, something it believes its target market of young women is particularly interested in. "Delicious sandwiches are no longer enough," says Cranks managing director Gavin Heys.
While the market has changed beyond recognition, it had not exactly been languishing before the focaccia revolution. The sandwich has always been a workaday staple - accounting for 41 per cent of the British fast- food market - it just hasn't always been very imaginative.
"The industry has pulled its socks up," says Mr Winship. "There's been a drive to build the market in quality terms, and the arrival of people like Boots has driven up standards across the board." As a result of consumer demand for higher quality, he says, the industry has just broken the culinary equivalent of the sound barrier: the pounds 3 sandwich. "Even a year ago people were saying that sandwiches would never go over pounds 3, but people are now quite happily spending that much, certainly in London."
Kick-started by niche players, the British market is now worth nearly pounds 3bn a year and is growing at an average annual rate of 5 per cent to 7 per cent, with some major sellers claiming growth rates more than three times that level.
With numbers like these being chalked up, it is no surprise that the industry has squeezed out some of the seedier independents and attracted big players angling for a lucrative slice. According to David Hallam, analyst at Williams de Broe, Marks & Spencer had 29 per cent of the market last year with sales of pounds 109m, followed by Tesco with pounds 71m and Boots with pounds 58m. Consumer demand for greater choice is the key factor driving the market.
"The days when people were satisfied with just cheese and pickle or ham are long gone," says Dave Robinson, marketing development manager at Boots, which has expanded its range to encompass tortillas and bagels. "People who usually go for fairly ordinary sandwiches will now also go for things that are a bit more of a treat."
In fact, they have improved so much that they are even attracting new fans on the continent. Hazlewood has set up factories in Germany and the Netherlands to exploit those markets, while Marks & Spencer is doing a roaring trade in the export of its British-made sandwiches to M&S branches in Germany and France.
Walk around Paris these days, and you will see that old British standby, the wedge sandwich, peeping out from the shelves of local grocery stores, edging out the baguettes. The old Earl would have been proud.