Can I stop US stock being sold on Amazon UK?
The labelling on a test buy tells you whether you've got a trademark case or a distribution problem. A UK trademark stops applying to goods once they've been put on the market in the UK or the European Economic Area with your consent, and consent given anywhere else doesn't count. So genuine stock bought at US retail and resold on amazon.co.uk can still infringe, as long as you hold a mark registered in the UK. Proper UK labelling points to your own distribution instead.

