This Instructable deals with mains power and will kill or horribly injure you if you don't know what you are doing. So unless you are a licensed electrician, don't do this yourself.
Step 1: Bits and Pieces
2x wall mounted double USB power points.
240v 10amp power cable. We got a nice cloth covered cable plus a little bit extra to join the power points.
Mains male plug.
Hunk of nice wood to mount everything on to.
Assorted electrical tools and tape.
Step 2: Prep
Strip back enough wire on both ends to comfortably fit in the plug. I had to go back after the photo and redo it.
***be very careful to check that you haven't inadvertently cut the insulating plastic on any of the wires - this is one of those things that leads to horrible injuries or death***
Connect your plug making sure all the wires have a good firm connection.
Strip out your chosen case and scrape/sand it back if necessary.
Step 3: Cut Out the Mounting Board
Mark out where you want the power points and test that all your devices and plugs will fit in the position.
Drill a hole in the middle (or a corner if you are confident not to screw it up) and use a jigsaw to cut out the spaces for mounting to sockets.
Test the spaces out and check the alignment of all the pieces several times as you go.
When everything fits and lines up, use a router (or Dremel in my case) and cut a line just deep and wide enough to run a cable between the two points.
Step 4: Lining the Case
Let it dry overnight with weights on it, then fold over the excess and repeat.
Once it is all dry use the spray adhesive to stick it in the case using offcuts of wood to clamp it in place while it dries.
Step 5: Putting It All Together
Wire together the two sockets and the mains plug taking particular care to match up the connectors to the matching position on the plug.
Use furniture brads to nail the mounting board in position.
Plug things in and test it out!