Be very careful if you join Amazon.co.uk and join prime and for any reason login to the Amazon.com site. I did that and they auto-joined me into Amazon.com Prime!!! Despite leaving .co.uk Prime before the trial period ended Amazon.com charged me $99 for my "ongoing subscription" IE I had left Amazon.co.uk prime but not amazon.com prime... It transpires Amazon.com and Amazon.co.uk have separate Prime memberships. Just on the chat now trying to get my money back!

[Edited on 13/5/15 by BenB]

If you cancelled quickly after they took payment they tend to refund (so long as you've not made use of the prime benefits in the period between payment being taken and cancellation) I had this happen with .co.uk a few years ago when I forgot to cancel at the end of a trial and cancelled a couple of days late!

They refunded me in the end. The annoying thing is I cancelled the Amazon.co.uk prime membership a full week before the end of the trial. However as they never made it obvious they'd kindly also enrolled me into Amazon.com prime I didn't know I had to cancel that separately. Bit cheeky if you ask me.
Quite why the enrolled me in Amazon.com prime I have no idea. Amazon.com won't post to the UK and you can't view any of the Prime Instant videos so why would someone in the UK want US Prime membership it's useless!

Yes I can see that. Certainly odd.

Caught my wife out the same way. She rang them and explained and they said they would refund. Their number is not so easy to find on the web site, however it is:

0800 496 1081

which is their general help line.

Beats me me why anyone would want it anyroad.
Cheers,
Bob