I have the earlier P2, which has no computer pocket and the web site does not mention one for the P3. You could fit a laptop between the case inserts and the outer cover, but there would not be any padding.
I can highly recommend this setup. I was driving across the Brooklyn bridge on my motorcycle at about 50 MPH with a full 4x5 kit, Gitzo tripod and about 50% of my DSLR kit in the P2 on the passenger seat. I forgot to strap it down! I heard a crash as I left the bridge and instantly knew that the bag was in the street behind me. Miraculously, the traffic was light (unusual for Manhattan at 8 PM) and no one ran over it. The backpack got a bit scrapped up from sliding along the pavement and the tripod and head were banged up, but functional. The backpack with lens and 4x5 camera cases functioned perfectly and there was no damage to the contents. I am very glad I purchased this system.