When amazon.co.uk links are used (as in this post) they are redirected incorrectly to the US site.
Links that are not to the US .com Amazon site will no longer be redirected there. We are not an affiliate in other countries.
Amazon links are rewritten to include an affiliate link for the network. At one point, the did geolocate, but stopped after a while.
It's a long story, but unless we operate a business in the UK, officially, we can't get affiliate income from Amazon there anyway .. so we don't geolocate amazon stuff any more, and have not for a while.
That answer also links to this blog post about SO's experiments with Amazon links and advertizing.