Surrounded by Farmfoods factories in an industrial estate in Cumbernauld near Glasgow in Scotland sits the Mackintosh factory, where skilled workers turn out coats for the Mackintosh label as well as some of the most prestigious fashion brands in the world.

The factory is basic, the roof is corrugated iron, the lighting harsh fluorescent; Miley Cyrus plays on the radio and there is a strong, overwhelming whiff of glue. The factory smells of glue because the traditional Mackintosh coats aren’t manufactured with sewing machines but instead are handmade, carefully put together by men, piece by piece, assembled using primitive-looking instruments and a gloopy adhesive, the product of skilled craftsmanship and traditional methods. The process seems almost rudimentary – the coatmakers apply the glue using their fingers before taping the seams and flattening them with a metal and wooden roller – but it is that very simplicity that makes it so sophisticated. Sewing machines are only used to attach trimmings after the coat has been assembled.

A man who wants to work as a coatmaker – and I say man because the coatmakers are all men; there are women employed in the factory too but they tend to work at the sewing machines – must spend two or three years learning the skills. ‘You can learn how to do it in three to six months,’ explains Lawrence Hammerton, who is 53 and works alongside his 18-year-old son Nicholas in the factory (sons following their fathers to Mackintosh isn't unusual), ‘but it takes two or three years to build up the stamina and the speed that you need.’ 

This is a factory full of perfectionists, they quietly go about their business, creating coats that haven’t changed much since the early 19th century, when Charles Macintosh (the ‘k’ in Mackintosh got added somewhere along the way) began manufacturing waterproof coats at his factory in Scotland, using a textile that consisted of two layers of fabric either side of a rubber sheet.

"Take a look through the archives at the factory and you’ll spot Hermes coats and Gucci coats and Balenciaga coats hanging on rails alongside rain-resistant uniforms and macs."

Certain business practicalities have changed for the Mackintosh brand along the way, however – the company is now owned by a Japanese firm – and as well as making coats for the Mackintosh brand, the factory creates outerwear for major fashion houses. Take a look through the archives at the factory and you’ll spot Hermès coats and Gucci coats and Balenciaga coats hanging on rails alongside rain-resistant uniforms and macs. Sometimes these collaborations have been private: Mackintosh produces coats for some of the most tight-lipped brands in international fashion, but others are more public, a celebration of two respected fashion brands joining forces.

A new Mulberry Mackintosh coat, which goes on sale next month, is a paradigm of that collaborative effort. Each coat was handmade at the Cumbernauld factory, using the traditional waterproof fabric and a bespoke pattern created by the Mulberry design team. The resulting coats manage to combine distinctive elements of each of their makers; there is that slight A-line shape so associated with Mackintosh but the trimmings and details are Mulberry through and through.

Buttons are decorative and there is a polka-dot fabric, something you rarely see with a Mackintosh coat: as all the waterproof rubberised fabric is produced in a Manchester factory that specialises in making convertible car roofs, a relatively tiny order of spotted waterproof fabric would have been difficult to obtain. The coats are a perfect pairing of two distinctly British brands, both famed for their outerwear, both well-known for their commitment to British manufacturing (Mulberry still makes many of its bags in its Somerset factory).

The Mulberry Mackintosh coats are sure to be popular in Britain but you can’t help but think that customers in Japan – Mackintosh consistently sells well there – and the US will love them wholeheartedly too, as they so perfectly encapsulate traditional British values of craftsmanship, history, design and practicality: never forget that no matter how sleek and stylish a Mackintosh mac is, it is always, above all, a raincoat. And what could be more British than that?    

The polka-dot Mulberry Mackintosh design is exclusive to Net-a-Porter and will be available to buy from 6 December; the plain design will be available from Mulberry in January 2014, See the Mulberry site for more details.