According to retail sources talking to CVG, if you want a PS4 pre-ordered and delivered on launch day in the UK, you're going to have to get in there and grab one before Monday next week. Apparently it's all to do with Sony not being able to produce enough PS4s to meet demand.
The effective deadline of August 5th was allegedly sent round to major retailers by Sony. That doesn't mean if you pre-order it later you absolutely won't get a console on release, but it looks decidedly unlikely given this little titbit.
Stores have been promised stock for sale on-the-day, though, so if you miss the pre-order window your best bet of grabbing one on day one is to queue overnight at your local store. You do still actually have a local gaming store right? [CVG]