Beneath it, a half shopping trolley appears to be crashing magically into the wall, heading in the direction of King’s Cross (and, presumably, Hogwarts).

The trolley is full of packaging along the lines of “Plastic Peas (is the product wasteful?)” or “Low Wage Watermelon (are the workers treated well?)”. And beside it is a banner advertising Provenance, one of the start-ups that’s just moved into the offices upstairs, and a company established to help us be better informed about the things we buy.

Inside the Tsuen Wan cotton mills being turned into creative arts hub

“Platform 9¾ is across the road behind our wall,” says Christian Layolle, Head of UK at The Mills Fabrica. “And, one day, we were thinking about how the founder of Provenance, Jessi Baker, had her aha moment in a supermarket looking at tins of tuna and thinking how they claim to be ethically fished, but how can consumers possibly know …”

“The platform at King’s Cross is where Harry Potter and the others enter their magical world,” Layolle continues. “And we thought that, although right now if consumers want to know more about products in a supermarket they hit a brick wall, with this technology you can travel right through it, and go on the journey to find out.”

There’s a section where you can scan yourself (in a changing room that recalls Japanese architect Shigeru Ban because of its use of cardboard poster tube as a construction material) for a pair of jeans that Hong Kong ethical start-up Unspun will make to your exact specification with a 3D loom, so it only weaves the width of fabric it needs.

“Most of the space is booked,” Layolle says. “Just the people aren’t actually in yet.”

And it’s lovely: clean lines; plenty of light; designer chairs; big, colourful conference tables (made by Dutch artist Dirk van der Kooij out of recycled CDs), chic recycled plastic carpet.

During an earlier phone interview, she told me how her grandfather had arrived in Hong Kong in 1949 along with hundreds of thousands of others fleeing the communist regime in China.

His family had been poor, but as a teenager he’d apprenticed with a cotton yarn maker in Ningbo, then Shanghai, and by the time he arrived in Hong Kong in his late 20s he was well placed to take advantage of generous government subsidies to encourage companies that would employ all those refugees.

When he set up Nan Fung Textiles in 1954, Chen specialised in denim, just as jeans were becoming fashionable. Later, in the 1960s (after the US and Britain introduced quotas to limit imports of cotton goods from Asia) Chen diversified into real estate, just as Hong Kong’s land prices were about to soar.

One day, aged 11, for a school project, Cheung asked her grandfather to show her his factory. By the mid 1990s, most textile factories in Hong Kong had closed, but three of Nan Fung’s mills in Tsuen Wan (Mills Four, Five and Six) were still operating.

“It was very dusty, I remember. And quite noisy,” she said. At the time she didn’t really know what to ask him about it, “so I didn’t, and that’s one of my biggest regrets.”

It was in part that dust and noise, in part it was growing up with certain expectations from the adults around her, and in part it was because she didn’t initially realise that the real business of Nan Fung was not in the mill but in the mind. But, for all these reasons, Cheung initially decided she wanted nothing to do with business at all.

“Grandpa only told us that it’s great to be a business-person but he never really explained why. And I have three siblings and so we’d shadow him in the office during summer holidays. But to me, it was really just boring,” said Cheung.

“I didn’t realise then that it’s all mental. It’s all about negotiation. And that bit you couldn’t see if you were shadowing someone.”

With the aim of becoming a veterinary surgeon – her childhood dream – she began by studying molecular biology at the University of California on the west coast of the United States. Doing that, she realised she was interested in structures of things, and so later, following her heart again, she studied landscape architecture at Harvard.

That led to an interesting thought. Perhaps she could reconfigure Mill Number Four – by then a warehouse – to become a space to inspire others to create businesses of the mind.

And if it was to do that, she wanted all the companies based there to have sustainability at their heart.

The Mills Fabrica Hong Kong opened in 2018, with a small textile museum and a batch of selected “incubatees”, all working on sustainable fashion and technology.

The Mills Fabrica London – backed by Nan Fung Group’s venture capital fund and its first overseas outpost – is planned to be the same (though without the museum). And if business thrives on space and connections, it’s chosen a promising location.

Further north, the foundations of the Google London headquarters are being dug into old railway land; to the west is the Francis Crick Institute, named after the discoverer of DNA; to the south are the British Library and the Wellcome Institute. A block away is the Institute of Physics.

It’s becoming known as the Knowledge Quarter. And the hope of many is that there, just moments away from the fictional Platform 9¾, transformations will occur – and that, in different ways, things that happen there will help the world get on track again.

Victoria Finlay’s book, Fabric: the Hidden History of the Material World, will be published in November