In the UK if you don't get certification for all electrical installations, commercial or domestic, good luck with your insurers. I also do product liability and fire claims, I've had $100m losses from a badly installed lightbulb. We had 43 lawyers/insurers in the room for the mediation. I also do work relating to Dangerous Substances and Explosive Atmosphere Regulations, where operators have to get detailed reports of every potential risk. The earliest risk I was involved with was a capsized oil rig with 138 lives lost. I did a Supreme Court case where the issue was steel certification of handlebars, which snapped and brain-injured my client, they met Japanese standards but not UK standards.I'm a lawyer, and I used to do a lot of defense of manufacturers in product liability claims.
Certification isn't required for some sales (depends on how and where the company is selling). And certification won't shield a company from liability.
With that said, we used to give clients the following advice:
1. If you sell enough stuff, and if it can presents any potential hazard, you'll eventually be sued. It doesn't even have to be for your product. We defended a bunch of fire cases where the fire started somewhere else. But our client's product was nearby, so that would be a target. (Often, the fires started in damaged extension cords. But it's often impossible to identify the manufacturer or seller of the cord, so plaintiffs' lawyers will sue someone with an identifiable product that's plugged into the extension cord.)
2. If you're sued, you need to be able to show that you (a) identified potential risks and (b) tried to design out any such risks. If you can't eliminate the risk by using an alternate design, then you guard against the risk. Finally, you warn about the risk, using appropriate warnings (where needed, when needed, etc.). We used to say that companies needed to create a "safety story." You don't want to create your safety story after the fact. Do it beforehand, and document it thoroughly.
In regard to these cables, I'm a bit concerned by the overlength ground pin. It seems possible that a user could insert the plug partway, resulting in a high-resistance connection at one of the other pins. And that could cause overheating and a subsequent fire.
If you look at outlets in enough houses, you'll see some that are a bit scorched, generally as a result of a high-resistance connection caused by partial insertion of a plug. (Sometimes the scorching is caused by a high-resistance connection in the male end of the cord.) And that's why, if your outlet starts feeling a bit sloppy, you should replace it.
(That sounds a bit . . . well . . .)
Broadly, the Supreme Court decided that the UK distributor is responsible, not the retailer. So if you buy a Topping amp on eBay delivered from China (which is how they do it) and it burns your house down, your are screwed. If they had a UK distributor, you could sue them.
What I've found is that if a UK distributor knows they have a product issue, they indemnify their dealers and tell them to screw their customers for as much as possible. So, for example, they will tell their customer "it's out of warranty, the cost is £2,000, but as an act of goodwill we'll fix it for you for £1,500". The dealer will have a happy customer and get the balance of £500 from the distributor. I've had this personally 3 or 4 times, went straight to the distributor on a few occasions (with Honda and Apple) about £4,000 of work cost me £0 and recently got a product upgrade at a 50% discount.
All of which is fine, but it is perfectly legal to sell a DIY cable kit. It will, however, have detailed wiring and safety instructions, so if you do a DIY cable and burn your house down, it's your own fault.
So in the UK product certification is not really what counts, it is much more important to know that the product is from a UK manufacturer or UK distributor. So buying a product shipped direct from China by the manufacturer offers no comfort at all.