I used to do the same as Jane, when leaving Bingley for even short periods I would (and still do really) take him out immediately before I left, just so he was empty. It's not an attention thing, if he is used to you being around pretty much all the time he is probably a bit anxious/stressed.
My partner and I both work, but we have managed to work things around Bingley. The only reason we've been able to get it to work is because we work quite different hours, meaning the longest period of no one being in the house is about four hours. Even so, this is too long to leave a young pup and so we had family/puppy sitters etc popping in and out. Now he is a bit bigger he actually goes to my MILs most days for those few hours. He loves to play with her dogs and she is only out for about an hour when he is with her. He's settled nicely into this routine now.
If he will only be 12/13 weeks when you go back to work, like Elaine has said, I would expect toilet training to go back quite a few steps. The simple fact is that most young puppies just cannot physically hold it for any prolonged length of time. I hope you have sorted out puppy sitters/family/dog walkers for when you go back to work. Again, as Elaine says, not wanting to sound harsh but you may find yourself facing many problems and issues if you have to continually leave your pup alone for extended periods of time. Now is the time you want to be working on leaving him for short periods, and arranging any day care/dog sitters you may need.
Good luck!