HTC One 32GB SIM Free shipped from Amazon UK for ~ $631
I personally thought the Android implementation from HTC was better than that from Samsung when I swapped my HTC for a S3 ages ago.
List price on Amazon.co.uk is £360.50 for the phone with £12.80 shipping. The warranty is obviously UK but I dont see that as an issue. Its pretty unlikely that its going to land at your door broken and if it does you just get a refund from Amazon - who has probably the best returns policy I've ever come across.