Amazon US are doing the Gear Fit watch for Samsung Galaxy devices (S4, S5, Note 3) for a pretty decent $99. Stock is due in 10/7 too.
In order to get the price, click on "32 used and new", then on the next page "All" and you'll see $99 from Amazon. Adding it is hit and miss but it's worth keeping an eye on certainly.
I understand Amazon.com items can be ordered to the UK, though there may be a delivery / customs charge. No idea on the warranty with Samsung and US products, sorry.