Ed Sheeran has a weirdly shaped head. It may harbour a brain that’s produced five number one singles, masterminded a multiple world-record-breaking album and earned a healthy £80 million (and counting), but in proportion it is not.“That’s the Shape of Ed,” Tom Davies grins as he hands me a prototype of the singer’s spectacles. The teal and charcoal acetate frame looks fine front-on, but from the side you can see how its arms twist in the most unlikely of angles – the right one veering slightly to one side and the left, significantly shorter one curving inwards, almost at a right angle. They look uncomfortable – verging on impossible – but I’m assured that they fit to perfection.

Tom Davies’ USP is frames shaped to fit both the wearer’s head and their lifestyle, made using materials that should, in theory, last a lifetime, and carved into designs that transcend seasonal trends – an antonym to the BOGOF deals that dominate the high street. His clients include Angelina Jolie, Heston Blumenthal and, yes, Ed Sheeran, all of whom frequent Davies’ stores for his signature specs.

“Understanding people and being able to read them is one of my top trumps,” the designer tells me. “Applying empathy to eyewear design is really important and that’s what my brand is all about: working out which frames suit which people, what they’re going to like wearing and what’s going to make them happy. It’s all about quality and fit.”

In his west London factory, a team of apprentices is being trained to master the painstaking, but surprisingly speedy, process that goes into a pair of Tom Davies frames. “This is ‘Bespoke-alator’ one,” Davies announces as he shows me around, fondly thumping a now-defunct machine, before showing me ‘Bespoke-alators’ five and eight, still in use. The state-of-the-art tech is used to speed up more menial tasks (such as cutting and binding the materials) before each pair of frames is passed to the craftsmen for polishing, tumbling and shaping. Elsewhere, there’s a separate machine for Davies’ series of horn specs, made from cattle horn farmed sustainably in India, Africa and the UK, and a special bench for his soon-to-be-launched gold- and silver-plated frames.

The factory opened at the end of last year, a twin to Davies’ original workspace in China. His craftsmen from abroad are teaching the new team the ropes; eventually the British workshop will produce 10,000 bespoke frames a month, each one taking just 22 hours to make.

“Being Made in England has got a huge marketing advantage,” Davies explains. “I opened a chain of opticians in Dubai and they weren’t interested. Now we’re Made in England, they can’t get enough of us. It’s the same in America; that’s my biggest growth market at the moment.”

The brand’s ready-to-wear frames will also be made in London, but it’s the bespoke service that is being given the utmost attention – and which, in turn, draws the crowd. “The shape of your nose is unique, so the chances of your glasses being identically shaped are almost impossible. That’s why people hate glasses. They don’t suit anyone,” says Davies. “I was serving a customer recently who had quite a strong brow line, and right at the end of our consultation I noticed his glasses were fogging up. I asked him about it and he said ‘yeah they always do’. We changed the angle of the frames to let the air come through, and now they don’t. That’s what bespoke is.”

The brand’s eye tests are equally extensive; while the typical optician will spend 15 minutes with a client, at Tom Davies they spend an hour, questioning their customers about their lifestyle, usage, posture and how they hold objects – all of this, Davies says, will affect your prescription.

“My stylist wears her glasses on the end of her nose because she has slight claustrophobia. But it means that her prescription changes,” says Davies. “A lot can depend on what you’re using them for too; I’ve been making Heston Blumenthal a diving mask, and we’ve given him a brand-new prescription that will work specifically for diving.”

So Ed Sheeran’s got a pair of specs to witness his sell-out stadium tours and Heston’s got a mask to see a submarine world; who does Davies most wish he could work with? “Prince William. There’s a reason he doesn’t like wearing his glasses, and it’s because they’re rubbish,” he laughs. “The future king needs a good pair of specs.”