“We’ve been in discussions with Valve about Assassin’s Creed 3 and Far Cry 3, but for the time being the games are not available via Steam in the UK. In the meantime, UK customers wishing to purchase either of these games can do so by visiting the Uplay store, our retail partners or other digital distributors. Assassin’s Creed 3 and Far Cry 3 are available on Steam in other regions outside the UK,” a statement advised.
Currently i'm mopping-up ACIII on my console of choice, whilst playing I started to get fed-up with the poor frame-rate... fortunately, I recently received a powerful-gaming PC, unfortunately, the best avenue for buying games on the PC is Steam and Ubisoft; in their infinite wisdom, have decided not to let Valve stock it. Ubisoft are, however, selling the game via their U-Play Service and Brick-&-Mortar stores, although i'm personally going to hold-out til they pull their head out of their collective asses and the game finds its way on the Steam service.
Far Cry 3 also affected.