If you've come through training like Making for Change, or you've simply been upcycling and mending for years and want to sell it, there's one legal distinction worth understanding before you take a stall: reselling a garment as-is is different, in law, from remaking one.
If you're buying secondhand clothes and selling them on unchanged, the street trading licence and insurance requirements I've written about elsewhere cover you, and secondhand clothes are commonly exempt from second-hand goods dealer registration. Upcycling changes that. Once you've substantially altered or remade a garment — patchworking, deconstructing and reconstructing, dyeing and reselling as a new piece — UK law can treat you as the manufacturer of that item, not just the seller of someone else's.
Under the Textile Products (Labelling and Fibre Composition) Regulations 2012, it's the manufacturer's responsibility to label fibre content — a durable, legible, visible label (a swing tag is fine) giving the exact percentage of any material making up more than 15% of the item's weight, with every material listed. For most one-off upcycled pieces this is genuinely manageable: know what you patched onto what, and say so on the tag.
Care labels aren't legally required the same way, but if you put one in, it becomes part of the item's legal description under current Trading Standards practice — so don't guess at a wash temperature you're not sure of. Getting it wrong is worse than leaving it off.
None of this is designed to put someone off selling handmade or upcycled clothing — it's the same basic honesty-in-labelling standard any new clothing brand has to meet, and it's genuinely achievable for a single trader with a sewing machine and a stall, not just a factory. Getting it right also separates you clearly from a casual secondhand seller in a buyer's eyes, which is exactly the story sustainable fashion is supposed to tell.
For everything else — the actual street trading licence, insurance, and Walthamstow specifically — see the full guide.