The UK has all sorts of extradition treaties with the US. Tell me you can't see Cameron shipping those he considers "undesirable", even folks on a holiday, off to the States if it suited his purpose?
Your pal's smarter than you, Your Grace.
This has absolutely zero to do with David Cameron and UK laws. There is no UK aspect to this at all. So let's simplify your argument:
Country A makes a regulation about a product.
Country B has no such regulation.
Country C also has no such regulation, but has an extradition treaty with country A.
Person in country B makes a product. It doesn't comply with country A's regulation. It doesn't have to, it's neither produced nor sold in country A.
Someone from country A visiting country B buys this product and takes it home with them. It has now "touched the shore" of country A.
Person from country B visits country C.
You propose that country C will arrest this person and extradite them at country A's request?