In cities like Amsterdam many of these unwanted bikes are left locked up outside. Owners simply can’t be bothered to take them away for scrap. Left to rust, these weesfietsen, or “orphan bikes”, create issues for municipal authorities fellow cyclists alike.

Not only are the abandoned bikes an eyesore, they clog up useful railings and bike racks in busy places like train stations, preventing others from using them. According to a 2014 study, 10 to 20 per cent of the bike parking spaces at Amsterdam stations are occupied by bikes whose owners will never retrieve them.

Removing them is an expensive and time-consuming process. “It costs around 50 euros per bike for a city to clear them”, Tiemen says. And such is the scale of the problem that it’s becoming a serious financial headache for Dutch municipal authorities. “There are over 80,000 bikes left abandoned every year in Amsterdam alone.”

Clearly the idea was one that would be good for the city, Tiemen explains. But it also offered a business opportunity. “It has a really good green business case around it. It’s environmentally very positive but it’s also economically interesting.”

So Tiemen and Mark set about rescuing orphaned bikes and working on how to recycle them. Getting hold of the bikes is the easy part, he tells me. The city tags locked bikes all the time, making regular collections of the ones that haven’t been moved for a prolonged period of time. “The good bikes they auction off so they reclaim some of the money but the other ones would normally go to scrap. We try to purchase them from the city.”

But if getting scrap bikes has proved relatively simple, surely recycling them into new bikes, especially nice new bikes that people are prepared to pay for, presents more problems? Surprisingly not, according to Tiemen. It took him and Mark nine months of development and testing to work it out but now the two and their team of builders have the process down.

It helps that they are selective about the bikes they buy. “There’s quite a wide range that we can handle but there are a lot of bikes that we can’t handle as well. We only do 28 inch wheels for example.”

They assess the steel frames they choose with “simple measuring tools,” before giving them a thorough visual inspection. Once a bike is back in their workshop and “the lacquer is cleared off, our visual inspection shows pretty much everything. When the frame is blasted down like that you can actually inspect it perfectly.”

So confident are Roetz in this inspection process that they actually provide a new warranty on all their bikes, despite the fact that the frames may be years or even decades old when they get them.

At the moment it’s just the frames that are re-used. But as you’d expect from a brand with recycling at its core, their other components are also sourced as responsibly (and as locally) as possible. “The leather for the saddle comes from Belgium. It’s taken from cows that have already been slaughtered for meat consumption. It is then handmade into a saddle in a little factory in the Netherlands which has been doing that for 100 years.

“The grips come from Portugal. They’re cork, and every seven years you can harvest cork off a tree, it doesn’t damage the tree – it just takes seven years to regrow. So that’s very low impact.

“The fenders and the chain guard we’ve developed ourselves and we try to source them as locally as possible. In the Netherlands there’s no local factory which could supply them but we’re doing them in Germany, so as locally as possible. They’re made from beech wood. The trees are harvested but they are replanted.”

Of course as a solution to the orphan bike problem none of this innovation, however noble the sentiments behind it, would be worth toffee unless the recycled bikes actually worked. Similarly, because they’re being marketed to fashionable young urbanites, the bikes need to look the part. Otherwise they risk becoming the cycling equivalent of a quorn sausage – very ethical, very well-intentioned, but actually a bit disgusting.

“The bikes need to look the part. Otherwise they risk becoming the cycling equivalent of a quorn sausage – very ethical but actually a bit disgusting.”

However I am given the chance to test-ride one of the Roetz Vigour models and thankfully I can report that it handles excellently. Not only that, it looks amazing too. The red rims, cream tyres and brown saddles turn more than a few heads as I cycle around the outdoor area of the bike trade show.

So have Roetz cracked it? Is this the answer to the issue of orphaned bikes in Amsterdam? And could their model offer a sustainable solution for future problems elsewhere?