The Sony Xperia X Performance launched in the US today $700, but Brits get it too.
Unlocked Mobiles has Black units in stock for £600 (including VAT). It has free next day delivery too. Hit the Source link to visit the store. Note that there's one seller on Amazon UK, but it dispatches from Hong Kong.
The official Sony Mobile site doesn't have a Buy button yet, not even Pre-order.
Courtesy yo GSMarena