Whilst the bulk of the brazing is completed by hand, the factory contains a fair few machines. Charlier shows me one such giant and explains: “All the main frame parts come in straight, they need to be bent. This machine has bent every bike frame since 1988. It’s done over 400,000 bike frames.”

They’ve also got a state of the art testing machine – which uses lasers to look for potential issues that could cause instability or failure. Despite the intricacies of a folding bike Brompton have had no major recalls – and Charlier puts much of that down to the machine, which is largely used by automotive companies: “We test one in 50 of the raw parts on this machine. The little red dot will go round and check the dimensions to make sure it’s built properly. If it’s slightly off, or not measured properly, it’s got serious implications down the line.We test one in 50 of brazed parts too, not to test the parts themselves but the brazing jigs. If one of the jigs [that the brazers use] was slightly off, we wouldn’t know until there had been a critical failure on that frame part.”

He adds: “We’ve never had any issues in terms of having to do a massive recall. As far as we know we’re the only bike manufacturer using one of these machines, they’re usually used by car manufacturers. The main reason we use it that a standard road bike has a little more room to flex, a carbon bike particularly. Because of all the folding parts we have to be extra careful. We don’t have that flex room to play with. A road bike you can flex around 0.3mm, we have about 0.01mm of flex – so basically none.”

The only brazing done via a machine is the process of attaching the hinge to the frame – Charlier says: “The main frame is brazed to a hinge. We built a machine ourselves to do that. It needs to be super strong, which is why we do it this way instead of by hand. There are very few machines in the factory compared to most bike brands.”

Once the key frame components are brazed and ready to go, they go into ‘rumblers’ – these machines heat up to 1000 degrees and buff up the metal by battering it with silicone pellets mixed with citric acid. Charlier is keen to point out that the materials are all biodegradable too “so can just throw out after”. He shows me the squeakily clean finished metal and I can’t help but internally comment that almost everything Brompton do seems to be notably squeaky clean in a literal and moral sense.

Once the metal is shiny to the upmost standards, it gets carried off in a lorry to Wales to be painted. When I ask why Wales, I’m told “we’ve just always used them” – but the painting job is soon to happen in house when a currently unused section of the factory has been developed – to cut down on time, fuel and money.

Painted parts sit in bays ready for assembly – and any piece of tubing with the tiniest mark is quarantined to be assessed and recycled. Charlier shows me one such part. The blemish is tiny and aesthetic – but he explains: “Every frame part is checked by hand, it has to be absolutely perfect. Our products are relatively expensive, so they have to go out absolutely perfect.”

I’m eye-poppingly surprised to hear that a finished bike is made from a total of 1,200 parts. My question: “are you including little bolts and stuff in that?!” is answered positively but it’s still a pretty incredible part total. Not only that, Charlier tells me that 99 per cent of those products are designed either by Brompton alone, or solely for use by Brompton and in conjunction with them.

When the bikes finally reach the assembly line, each one is treated as an individual. Literally. Bikes are specced by the potential owner, down to handlebar shape, gearing, accessories and of course colour. Each bike has it’s own requirement sheet – a DNA sheet for the bike effectively – and when each piece of the puzzle is complete it’s scanned and sent to the next builder. It’s an intricate process, but from start to finish takes just 3.5 minutes, with an average of 150 bikes built a day.

Of course, all this expansion can’t be just for giggles. Brompton is going places. Currently they make 47,000 bikes a year, selling to 44 countries, 30 per cent in Europe and 55 per cent of UK bikes being bought in London. Their next big project? Electric folding bikes.

Charlier tells me: “They’re huge in Germany and elsewhere; the UK is a bit behind. Our bikes will use pedal assist – which means you still have to pedal for them to work. You might be a bit faster on the flat, and hills will feel like flat ground. We’ve made them to be city bikes – you will be able to plug the battery into your laptop to charge whilst you’re working, and charge your laptop whilst cycling. They’re going to be amazing.”

They do sound pretty cool – and we look forward to playing the ‘whose Brompton has an electric motor’ game at a London roadside cafe near you soon.