TalkTalk are not a good ISP by anyone's assessment. I would not be at all surprised if they see your router connected idle and time it out and disconnect you.
I believe this is your problem. Try chaining a load of massive, massive downloads before you go out to work and see if it is still connected and running when you return home. If this fails, let me know and I can try and think of something else.
Born London, Live London, Die London
As a Londoner, I exercise my God given Right to do as I please