UK carrier EE has exclusivity on the Arctic Silver color option of the Samsung Galaxy S8 and has now started taking pre-orders. Its best-selling plan sees you paying £30 up front for the phone and then £48 a month for two years. You're getting unlimited texts/calls and 2GB of data. Again, this is a pre-order, the phone will be dispatched within 14 days. There's no SIM-free option, however. Amazon UK does have some units, the cheapest of which is £513 + £17 delivery. Note that these usually ship from Italy. Source
Source: http://www.gsmarena.com/ee_now_taking_preorders_for_samsung_galaxy_s8_in_arctic_silver-news-25705.php