It doesn't work that way due to tax, hence the official price is £10.99Unless I'm stupid it's £10.99 today right...? Now go to the release announcement on steam: https://steamcommunity.com/games/255710/announcements/detail/710835733887738441 (or above in the thread OP's post)
$14.99 which currently in the United Kingdom is £12.01. If our pound is stronger it will be cheaper I suppose but if the pound drops then that price goes up.
I still don't understand why we cannot preorder it on Steam or GMG just yet.