I am watching this at the moment on NOW TV... I think you have to buy some sort of box to connect to your TV, but I have it on my Smart TV as an app... If you google NOW TV and go to their website, I think you may be able to pay the monthly fee and watch it on your PC/laptop??
OK, I just logged into my NOW account on PC and yes, you can watch it. If you sign up and choose the Entertainment pass, it is £4.99 for one month and they are currently showing seasons 1-3 of Game of Thrones. Enjoy... its brilliant!