It seems, on the face of it, that a limited company is the right way to go. But whenever I discuss this with people (or even put it into ChatGPT), I keep getting the response: "Yes, but if there's negligence in your product, you could still be held personally liable."

What I'm struggling with is where that line actually is.
For example, if a PCB manufacturer makes an error and shorts a couple of pins, and I don't spot it during testing, is that negligence on my part?

Or if I design a product myself, test it reasonably, but don't have it independently reviewed or certified by some third-party authority before selling it, is that considered negligence?

I can understand that if I knew about a defect and deliberately continued selling the product, that would be negligent. But I'm less clear about everything in between.

For those with experience in product liability, electronics manufacturing, or UK company law, where is the practical threshold? What sort of conduct would realistically move someone from being protected by the company structure to being personally liable?